You’re going on a shopping trip! But you only have a certain amount of money to spend.

Write a function that takes in:
1. budget: the total amount of money you have to spend,
2. num_items: the number of items you want to buy,
3. avg_costs: a dictionary where the keys are store names and the values are the average cost per item at each store.

The function should return a list of store names where you can afford to buy the number of items within your budget. You can afford a store if the total cost (number of items * average cost per item) is less than or equal to your budget.

budget = 100
num_items = 5
avg_costs = {"Store A": 15, "Store B": 30, "Store C": 18}

# The total cost at Store A is 15 * 5 = 75, which is within the budget.
# The total cost at Store B is 30 * 5 = 150, which exceeds the budget.
# The total cost at Store C is 18 * 5 = 90, which is within the budget.

# So, the function should return ["Store A", "Store C"]