If a book costs $15 and you buy 4, how much do you spend?

To determine the total amount spent on the books, you need to multiply the cost of one book by the number of books purchased. In this case, each book costs $15, and you want to buy 4 books.

Performing the calculation:

Total cost = Price per book × Number of books

Total cost = $15 × 4 = $60

Thus, when you purchase 4 books at $15 each, you end up spending a total of $60. This is the correct answer, as it accurately reflects the multiplication of the unit price by the quantity bought.