Reasoning and answer: On Thursday 15 * 3 = 45 books were sold. On Friday 45 / 5 = 9 books were sold. Adding up all three days 15 + 45 + 9 = 69 books were sold by Friday.
The answer: 69
What was the question?
Question: A new book sold 15 copies at the bookstore on Wednesday. On Thursday the book sold three times that many copies. On Friday the book sold one-fifth the number of copies it did on Thursday. How many copies of the book did the bookstore sell by Friday?

Reasoning and answer: The second pair of shoes was 50 / 100 * 22 = $11 more expensive. That means that the second pair's price was 22 + 11 = $33. So for both pairs of shoes, Nina paid 33 + 22 = $55.
The answer: 55
What was the question?
Question: Nina has two pairs of shoes. She bought one of them for $22, and the second one was 50% more expensive. How much did Nina pay for both pairs of shoes?

Reasoning and answer: Amount spent on textbooks is 960 / 2 = 480 dollars. Amount spent on school supplies is 480 / 4 = 120 dollars. Amount Derek has left 960 - 480 - 120 = 360 dollars.
The answer: 360
What was the question?
Question:
Derek has $960 to buy his books for the semester. He spends half of that on his textbooks, and he spends a quarter of what is left on his school supplies. What is the amount of money Derek has left?