Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.
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Question: Problem: if 12 machine can finish a job in 40 days, then how many more machines would be needed to finish the job in one - fourth less time ?
Options: a. a. 4, b. b. 8, c. c. 10, d. d. 12, e. e. 16

Answer: a

Question: Problem: a can do a job in 15 days and b in 20 days. if they work on it together for 4 days, then the fraction of the work that is left is ?
Options: a. 2 / 15, b. 8 / 15, c. 3 / 11, d. 1 / 12, e. 6 / 13

Answer: b

Question: Problem: a car salesman earns a base salary of $ 1000 per month plus a commission of $ 200 for each car he sells. if the car salesman earned $ 2000 in march, how many cars does he need to sell in april in order to double his march earnings ?
Options: a. 14, b. 15, c. 16, d. 17, e. 18

Answer:
b