Challenge 1: Bank Account Class — Possible Solution
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class BankAccount:
    def __init__(self, owner, balance=0):
        self.owner = owner
        self.balance = balance

    def deposit(self, amount):
        self.balance += amount

account = BankAccount("Ada")
account.deposit(100)
account.deposit(50)

print(account.balance)

Output:
150

WHY THIS WORKS AS AN ANSWER
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__init__(self, owner, balance=0) reuses two things from earlier
chapters at once: the self.x = ... instance-attribute pattern from
this chapter, and the default-parameter-value syntax from Course 1
Chapter 8 — balance=0 means BankAccount("Ada") alone is a valid call,
with balance falling back to 0 automatically.

deposit(self, amount) is an ordinary method, taking self (this
chapter's explicit first-parameter convention) plus the amount to add.
self.balance += amount reads and rewrites the SAME instance's balance
attribute — since balance was set via self.balance in __init__, it's
an instance attribute unique to this one account object, not shared
across other BankAccount instances the way this chapter's
warn-box-covered class attributes would be.

Calling account.deposit(100) then account.deposit(50) runs that method
twice against the same account object, so the two deposits accumulate:
0 + 100 + 50 = 150.