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.

Q: Problem: a fort had provision of food for 150 men for 45 days. after 10 days, 25 men left the fort. find out the number of days for which the remaining food will last.
Options: a. 44, b. 42, c. 40, d. 38, e. 36

A: b
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Q: Problem: the speed of the boat in still water in 12 kmph. it can travel downstream through 54 kms in 3 hrs. in what time would it cover the same distance upstream ?
Options: a. 8 hours, b. 6 hours, c. 4 hours, d. 5 hours, e. 9 hours

A: e
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Q: Problem: find the compound interest on $ 1000 in 2 years at 4 % per annum, the interest being compounded half - yearly ?
Options: a. $ 645.56, b. $ 82.43, c. $ 954.26, d. $ 745.69, e. $ 1020.45

A:
b
****