Melanie had 255 dollars to spend on 8 books. after buying them she had 15 dollars. how much did each book cost?

Okay, so the answer should be $30 for each book. I have a picture to show you. :D 

1. She starts with $255.

2. She purchases 8 books for an unknown cost per book, so she spends 8 * (unknown cost per book).

3. She is left with $15. 

Let's set up an equation:





Now, we solve. First, we'll subtract 255 from each side:



Now, we'll divide through by -8:



The cost per book is $30. Let's check it out:

$30/book * 8 books = $240

She started with $255 and spent $240, which leaves her with $15. Exactly what the original question indicated. We're done. (Those are some expensive books.)