Peter and Kristin are to read 20 fantasy novels each in a week. Peter can read three times as fast as Kristin. If Peter reads one book in 18 hours, how long will Kristin read half of her books? Give the rationale and then the answer.
Let's think step by step. Since Peter reads three times as fast as Kristin, Kristin will take 18 * 3 = 54 hours to read one book. Kristin reads half of her books, a total of 20 / 2 = 10 books. The time Kristin will take to read half of her books is 10 * 54 = 540.. The answer is: 540.

Nadia is learning to play the piano. She normally makes 3 mistakes per 40 notes and can play about 60 notes a minute.  If she plays for 8 minutes how many mistakes will she make on average? Give the rationale and then the answer.
Let's think step by step. She plays 480 notes because 8 x 60 = 480. This is 12 blocks of 40 notes because 480 / 40 = 12. She makes 36 mistakes because 12 x 3 = 36.. The answer is: 36.

Walter works 5 days a week in a fast-food chain and earns $5 per hour. Since he is a working student, he can only work 4 hours a day and allocates 3/4 of his weekly earning for his schooling. How much does he allocate for school? Give the rationale and then the answer.

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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Let's think step by step. Walter's daily earning is $5 x 4 = $20. So he earns $20 x 5 = $100 per week. Therefore, he allocates $100 x 3 / 4 = $75 for his school.. The answer is: 75.