diff --git a/src/part4/cart.py b/src/part4/cart.py
index aed9bb72..4851330d 100644
--- a/src/part4/cart.py
+++ b/src/part4/cart.py
@@ -9,7 +9,7 @@
 an explanatory message to stdout and returns ``None``.
 """
 
-from .storage import Product
+from .storage import QUANTITY_KEY, Product
 
 
 # TODO: при необходимости добавьте свои вспомогательные функции
@@ -47,7 +47,22 @@ def add_to_cart(
         request.
     """
     # TODO: реализуйте функцию
-    return 0
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+    quantity_old = storage[product_id][QUANTITY_KEY]
+    if quantity_old < quantity:
+        print(
+            f"not enough stock for product {product_id}: {quantity_old} available, {quantity} requested"
+        )
+        return None
+    storage[product_id][QUANTITY_KEY] = quantity_old - quantity
+    if product_id in cart:
+        cart[product_id] += quantity
+    else:
+        cart[product_id] = quantity
+
+    return cart[product_id]
 
 
 def remove_from_cart(
@@ -84,4 +99,21 @@ def remove_from_cart(
         the cart does not hold the product or holds too few units.
     """
     # TODO: реализуйте функцию
-    return 0
+    if product_id not in cart:
+        print(f"product {product_id} is not in the cart")
+        return None
+    if cart[product_id] < quantity:
+        print(
+            f"cart holds only {cart[product_id]} unit(s) of product {product_id}, "
+            f"cannot remove {quantity}"
+        )
+        return None
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+    cart[product_id] -= quantity
+    storage[product_id][QUANTITY_KEY] += quantity
+    if cart[product_id] == 0:
+        del cart[product_id]
+        return 0
+    return cart[product_id]
diff --git a/src/part4/crud.py b/src/part4/crud.py
index 471eff00..71f9ab9c 100644
--- a/src/part4/crud.py
+++ b/src/part4/crud.py
@@ -23,16 +23,16 @@
 than a scan over ``storage.values()``.
 """
 
-import uuid  # noqa: F401
+import uuid
 from typing import Any
 
-from .storage import (  # noqa: F401
+from .storage import (
     NAME_KEY,
     PRICE_KEY,
     QUANTITY_KEY,
     Product,
 )
-from .utils import normalize_price, normalize_product_name  # noqa: F401
+from .utils import normalize_price, normalize_product_name
 
 
 def generate_product_id() -> str:
@@ -42,7 +42,7 @@ def generate_product_id() -> str:
         A freshly generated UUID, stringified.
     """
     # TODO: реализуйте функцию
-    return ""
+    return str(uuid.uuid4())
 
 
 def create_product(
@@ -74,7 +74,22 @@ def create_product(
         message is printed.
     """
     # TODO: реализуйте функцию
-    return ""
+    name, price, quantity = fields[NAME_KEY], fields[PRICE_KEY], fields[QUANTITY_KEY]
+    normalized_name = normalize_product_name(name)
+    if not normalized_name:
+        print("product name must not be blank")
+        return None
+    if normalized_name in product_names:
+        print(f"product name '{normalized_name}' is already taken")
+        return None
+    newuuid = generate_product_id()
+    storage[newuuid] = {
+        NAME_KEY: normalized_name,
+        PRICE_KEY: normalize_price(price),
+        QUANTITY_KEY: quantity,
+    }
+    product_names.add(normalized_name)
+    return newuuid
 
 
 def read_product(storage: dict[str, Product], product_id: str) -> Product | None:
@@ -89,7 +104,10 @@ def read_product(storage: dict[str, Product], product_id: str) -> Product | None
         that identifier (a message is printed in that case).
     """
     # TODO: реализуйте функцию
-    return {}
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+    return storage[product_id]
 
 
 def update_product(
@@ -129,8 +147,30 @@ def update_product(
         and an explanatory message is printed. Renaming a product to its
         own current name is allowed.
     """
-    # TODO: реализуйте функцию
-    return {}
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+    name_old = storage[product_id][NAME_KEY]
+    if NAME_KEY in fields:
+        normalized_name = normalize_product_name(fields[NAME_KEY])
+        if not normalized_name:
+            print("product name must not be blank")
+            return None
+        if normalized_name != name_old and normalized_name in product_names:
+            print(f"product name '{normalized_name}' is already taken")
+            return None
+        storage[product_id][NAME_KEY] = normalized_name
+        fields[NAME_KEY] = normalized_name
+        if name_old != normalized_name:
+            product_names.remove(name_old)
+            product_names.add(normalized_name)
+    if PRICE_KEY in fields:
+        normalized_price = normalize_price(fields[PRICE_KEY])
+        fields[PRICE_KEY] = normalized_price
+        storage[product_id][PRICE_KEY] = normalized_price
+    if QUANTITY_KEY in fields:
+        storage[product_id][QUANTITY_KEY] = fields[QUANTITY_KEY]
+    return storage[product_id]
 
 
 def delete_product(
@@ -154,4 +194,10 @@ def delete_product(
         are left unchanged and a message is printed).
     """
     # TODO: реализуйте функцию
-    return ""
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+    name = storage[product_id][NAME_KEY]
+    del storage[product_id]
+    product_names.remove(name)
+    return product_id
diff --git a/src/part4/run_admin.py b/src/part4/run_admin.py
index 2247b29b..cdc16529 100644
--- a/src/part4/run_admin.py
+++ b/src/part4/run_admin.py
@@ -28,22 +28,36 @@
 is left untouched and the loop keeps running; only ``exit`` stops it.
 """
 
-from decimal import Decimal, InvalidOperation  # noqa: F401
+from decimal import Decimal, InvalidOperation
 from typing import Final
 
-from .crud import (  # noqa: F401
+from .crud import (
     create_product,
     delete_product,
     read_product,
     update_product,
 )
-from .storage import NAME_KEY, PRICE_KEY, QUANTITY_KEY, Product  # noqa: F401
-from .utils import get_storage_str_representation  # noqa: F401
+from .storage import NAME_KEY, PRICE_KEY, QUANTITY_KEY, Product
+from .utils import get_storage_str_representation
 
 
 # TODO: задайте приглашение и текст справки (используйте своё решение части 3)
-PROMPT: Final[str] = ""
-HELP_TEXT: Final[str] = ""
+
+
+PROMPT: Final[str] = "admin> "
+
+HELP_TEXT: Final[str] = """Available commands:
+  help                                       show this message
+  exit                                       leave the console
+  show                                       print the whole store as a table
+  create <name...> <price> <quantity>        add a product, print its new id
+  read <id>                                  print the product with that id
+  update <id> <name...> <price> <quantity>   overwrite that product's fields
+  delete <id>                                remove the product with that id
+
+For create and update the price and quantity are the last two words of the
+line; everything before them is the product name, so it may contain spaces
+(for example "Gibson SG Junior") and needs no quoting."""
 
 
 def show_help() -> None:
@@ -53,7 +67,7 @@ def show_help() -> None:
     is: a heading, one line per command with a short description, and a
     note on how multi-word names are parsed.
     """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
+    print(HELP_TEXT)
 
 
 def print_result(result: object) -> None:
@@ -64,7 +78,8 @@ def print_result(result: object) -> None:
             operation already reported its own failure, so nothing is
             printed in that case.
     """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
+    if result is not None:
+        print(result)
 
 
 def run_command(
@@ -92,7 +107,40 @@ def run_command(
             ``update`` does not parse as a decimal number.
     """
     # TODO: реализуйте функцию
-    return False
+    match line.split():
+        case ["read", product_id]:
+            print_result(read_product(storage=storage, product_id=product_id))
+        case ["delete", product_id]:
+            print_result(
+                delete_product(
+                    storage=storage, product_names=product_names, product_id=product_id
+                )
+            )
+        case ["create", *name, price, quantity] if name:
+            product_name = " ".join(name)
+            fields = {
+                NAME_KEY: product_name,
+                PRICE_KEY: Decimal(price),
+                QUANTITY_KEY: int(quantity),
+            }
+            print_result(create_product(storage, product_names, fields))
+        case ["update", product_id, *name, price, quantity] if name:
+            product_name = " ".join(name)
+            fields = {
+                NAME_KEY: product_name,
+                PRICE_KEY: Decimal(price),
+                QUANTITY_KEY: int(quantity),
+            }
+            print_result(update_product(storage, product_names, product_id, fields))
+        case ["show"]:
+            print(get_storage_str_representation(storage))
+        case ["exit"]:
+            return False
+        case ["help"]:
+            show_help()
+        case _:
+            print(f"'{line}' is not a command")
+    return True
 
 
 def main() -> None:
diff --git a/src/part4/storage.py b/src/part4/storage.py
index 9acedf07..a25f6253 100644
--- a/src/part4/storage.py
+++ b/src/part4/storage.py
@@ -40,6 +40,6 @@
 
 # Name of each field inside a Product record.
 # TODO: задайте имена полей записи
-NAME_KEY: Final = ""
-PRICE_KEY: Final = ""
-QUANTITY_KEY: Final = ""
+NAME_KEY: Final = "name"
+PRICE_KEY: Final = "price"
+QUANTITY_KEY: Final = "quantity"
diff --git a/src/part4/utils.py b/src/part4/utils.py
index d2a940ea..4c0f4a35 100644
--- a/src/part4/utils.py
+++ b/src/part4/utils.py
@@ -18,10 +18,10 @@
   the longest value it holds in that particular call.
 """
 
-from decimal import ROUND_HALF_UP, Decimal  # noqa: F401
+from decimal import ROUND_HALF_UP, Decimal
 from typing import Final
 
-from .storage import (  # noqa: F401
+from .storage import (
     NAME_KEY,
     PRICE_KEY,
     QUANTITY_KEY,
@@ -33,14 +33,14 @@
 # Quantisation step derived from PRICE_PRECISION, e.g. Decimal("0.01").
 # TODO: задайте число знаков после запятой и шаг квантования (используйте своё
 # решение части 3)
-PRICE_PRECISION: Final[int] = 0
-PRICE_STEP: Final = Decimal(0)
+PRICE_PRECISION: Final[int] = 2
+PRICE_STEP: Final[Decimal] = Decimal(1).scaleb(-PRICE_PRECISION)
 
 # Column headers of the table produced by get_storage_str_representation,
 # left to right. The width of each column is not fixed here -- it is
 # measured per call from the data (see the function).
 # TODO: задайте заголовки столбцов таблицы (используйте своё решение части 3)
-TABLE_HEADERS: Final[tuple[str, ...]] = ()
+TABLE_HEADERS: Final[tuple[str, ...]] = ("ID", "name", "price", "quantity")
 
 
 def normalize_price(price: Decimal) -> Decimal:
@@ -53,8 +53,7 @@ def normalize_price(price: Decimal) -> Decimal:
         ``price`` quantised to :data:`PRICE_PRECISION` fractional digits,
         with halves rounded up.
     """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
-    return Decimal(0)
+    return price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP)
 
 
 def normalize_product_name(name: str) -> str:
@@ -71,8 +70,10 @@ def normalize_product_name(name: str) -> str:
         The result is an empty string when ``name`` holds nothing but
         whitespace.
     """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
-    return ""
+    list_of_words = name.split()
+    name = " ".join(list_of_words)
+    name = name.lower()
+    return name
 
 
 # TODO: при необходимости добавьте свои вспомогательные функции
@@ -97,4 +98,23 @@ def get_storage_str_representation(storage: dict[str, Product]) -> str:
         returned, sized to the header labels.
     """
     # TODO: реализуйте функцию (используйте своё решение части 3)
-    return ""
+    mxlen1 = len(TABLE_HEADERS[0])
+    mxlen2 = len(TABLE_HEADERS[1])
+    mxlen3 = len(TABLE_HEADERS[2])
+    mxlen4 = len(TABLE_HEADERS[3])
+    for item_id, product in storage.items():
+        name = str(product[NAME_KEY])
+        price = str(product[PRICE_KEY])
+        quantity = str(product[QUANTITY_KEY])
+        mxlen1 = max(mxlen1, len(item_id))
+        mxlen2 = max(mxlen2, len(name))
+        mxlen3 = max(mxlen3, len(price))
+        mxlen4 = max(mxlen4, len(quantity))
+    s1 = f"| {TABLE_HEADERS[0].ljust(mxlen1)} | {TABLE_HEADERS[1].ljust(mxlen2)} | {TABLE_HEADERS[2].ljust(mxlen3)} | {TABLE_HEADERS[3].ljust(mxlen4)} |"
+    s2 = f"|{'-' * (mxlen1 + 2)}|{'-' * (mxlen2 + 2)}|{'-' * (mxlen3 + 2)}|{'-' * (mxlen4 + 2)}|"
+    snext = [
+        f"| {str(item_id).ljust(mxlen1)} | {str(product[NAME_KEY]).ljust(mxlen2)} | {str(product[PRICE_KEY]).ljust(mxlen3)} | {str(product[QUANTITY_KEY]).ljust(mxlen4)} |"
+        for item_id, product in storage.items()
+    ]
+    rows = [s1, s2, *snext]
+    return "\n".join(rows)