He paid for 20 / 10 = 2 hours. That means the hourly fee was 30 * 2 = $60. So the total cost was 60 + 20 = $80.
The answer: 80
Reverse engineering the question: Jefferson hires a carriage to go to the church. It is 20 miles away. The horse can go 10 miles per hour. It cost $30 per hour plus a flat fee of $20. How much did he pay for the carriage?


Reasoning and answer: First figure out how much the first babysitter costs by multiplying her hourly rate by the number of hours she works: $16 / hour * 6 hours = $96. Then use the same method to figure out how much the second babysitter charges before any screaming: $12 / hour * 6 hours = $72. Then figure out how much the babysitter charges for two screams: 2 screams * $3 / scream = $6. Finally, subtract the second babysitter's two charges from the first babysitter's total charge to find the difference: $96 - $72 - $6 = $18.
The answer: 18
What was the question?
Question: Milly's babysitter charges $16/hour. Milly is considering switching to a new babysitter who charges $12/hour, but also charges an extra $3 for each time the kids scream at her. If Milly usually hires the babysitter for 6 hours, and her kids usually scream twice per babysitting gig, how much less will the new babysitter cost?


In the first verse, 30 / 2 = 15 singers sang. In the second verse, 15 / 3 = 5 singers joined in. In the final verse, 30 - 15 - 5 = 10 singers joined for the whole choir to sing together.
The answer: 10
Reverse engineering the question: A choir was singing a song that involved 30 singers. In the first verse, only half of them sang. In the second verse, a third of the remaining singers joined in. How many people joined in the final third verse that the whole choir sang together?


Reasoning and answer: There are 30 x 5 = 150 stamps on each of the first 10 pages. So she has a total of 150 x 10 = 1500 stamps in the first 10 pages. There are 50 - 10 = 40 pages that have 50 stamps each. There is a total of 40 x 50 = 2000 stamps in the remaining 40 pages. Therefore, Stella has 2000 + 1500 = 3500 stamps in her album.
The answer: 3500
What was the question?
Question: Stella collects stamps. She counted 50 pages in her collector's album. There are 5 rows of 30 stamps in each of the first 10 pages of her album. The rest of the pages each have 50 stamps. How many stamps are in Stella's album?


If there are 2800 calories in every cheesecake, and each slice of cheesecake contains 350 calories, then the cheesecake has 2800 / 350 = 8 slices. If Kiley ate 25% of the cheesecake, then she ate 8 * 0.25 = 2 slices of cake.
The answer: 2
Reverse engineering the question: Each slice of cheesecake contains 350 calories. If there are a total of 2800 calories in every cheesecake, and Kiley ate 25% of the cheesecake, how many slices of cheesecake did Kiley eat?


If Roselyn gave Rebecca 40 books, and Mara was given three times as many books, Mara has 3 * 40 = 120 books. Rebecca and Mara's total number of books is 120 + 40 = 160 books. If Roselyn gave Mara and Rebecca her books, which is 160, then she initially had 60 + 160 = 220 books.
The answer: 220
Reverse engineering the question:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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Roselyn gives Mara three times as many books as she gives Rebecca and remains with 60 books. If Rebecca received 40 books, how many books did Roselyn have before?