Aman buys four books from the store and a preferred reader discount card for $20. later that day, he goes back and buys five more books. he also got $5 discount using his new card. if he spent a total of $87 at the bookstore, how much did each book cost assuming every book cost the same amount?

Let x be the cost of each book.

So, the cost of 4 books is 4x.

For the purchase of 4 books, he got a discount of $20.

So, the amount he paid for the first four books = 4x - 20.

Now, the cost of 5 books is 5x.

For the purchase of 5 books, he got another discount of $5.

So, the amount he paid for the five books = 5x - 5.

Total money spent = $87.

Therefore, (4x - 20) + (5x - 5) = 87

4x + 5x - 20 - 5 = 87

9x - 25 = 87

9x = 87 + 25

9x = 112

Divide both sides by 9.

x = 12.4

Hence, the cost of each book = $12.4.