Carla purchases for books for $10 amy purchase nine books how much did amy spend if her books cost the same as carla’s

Let's find out the cost of one book. Carla bought 4 for $10, so each book costs:

=$2.50

Amy bought 9 books, so to find out how much she spent, multiply 9 by the price of $2.50.

9×2.50 = $22.50