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

To determine the total cost of purchasing 4 books that each cost $15, you need to multiply the price of one book by the number of books being bought. This calculation is expressed as:

Total Cost = Price per Book × Number of Books

Substituting the values from the question:

Total Cost = $15 × 4

Calculating this gives:

Total Cost = $60

Thus, when you buy 4 books at $15 each, you will spend a total of $60. This is why the answer is correct and matches the option indicating $60 as the total expenditure.