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: the speed of the boat in still water in 12 kmph. it can travel downstream through 48 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. 6 hours

A: e
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Q: Problem: two trains travel in opposite directions at 36 kmph and 45 kmph and a man sitting in slower train passes the faster train in 8 seconds. the length of the faster train is
Options: a. 80 m, b. 100 m, c. 120 m, d. 180 m, e. 160 m

A: b
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Q: Problem: a runner runs the 40 miles from marathon to athens at a constant speed. halfway through the run she injures her foot, and continues to run at half her previous speed. if the second half takes her 8 hours longer than the first half, how many hours did it take the runner to run the second half ?
Options: a. 10, b. 12, c. 16, d. 20, e. 24

A:
c
****