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.

Example Input: Problem: a 11 % stock yields 8 %. the market value of the stock is :
Options: a. rs. 72, b. rs. 137.50, c. rs. 112.50, d. rs. 116.50, e. none of these
Example Output: b

Example Input: 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
Example Output: e

Example Input: Problem: a train travels from new york to chicago, a distance of approximately 270 miles, at an average rate of 30 miles per hour and arrives in chicago at 6: 00 in evening, chicago time. at what hour in the morning, new york time, did the train depart for chicago ? ( note: chicago time is one hour earlier than new york time.
Options: a. 3: 00, b. 4: 00, c. 10: 00, d. 6: 00, e. 7: 00
Example Output:
c