Answer: $8 flat rate
Step-by-step explanation: First subtract 24.50 from 48.50 to find the amount that was charged for the 3 additional books.
48.50 - 24.50 = 24
So the remaining 3 books costed a total of $24
Next, we need to divide 24 by 3 to determine how much each additional book costs.
24/3 = 8
So, the flat rate after the first book is purchased is $8 per additional book.