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.

[EX Q]: Problem: a student travels from his house to school at 10 km / hr and reaches school 2 hours late. the next day he travels 18 km / hr and reaches school 1 hour early. what is the distance between his house and the school ?
Options: a. 65.0, b. 67.5, c. 70.0, d. 72.5, e. 75.0
[EX A]: b

[EX Q]: 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
[EX A]: a

[EX Q]: Problem: a collection of books went on sale, and 2 / 3 of them were sold for $ 4.25 each. if none of the 30 remaining books were sold, what was the total amount received for the books that were sold ?
Options: a. $ 260, b. $ 255, c. $ 285, d. $ 290, e. $ 275
[EX A]:
b