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 Input:
Problem: a man sitting in a train which is traveling at 36 kmph observes that a goods train, traveling in opposite direction, takes 10 seconds to pass him. if the goods train is 240 m long, find its speed
Options: a. 50 kmph, b. 56 kmph, c. 58 kmph, d. 62 kmph, e. 72 kmph

Ex Output:
a

Ex Input:
Problem: what is the rate percent when the simple interest on rs. 810 amount to rs. 155 in 4 years ?
Options: a. 4.78, b. 4.68, c. 4.58, d. 4.48, e. 4.38

Ex Output:
a

Ex Input:
Problem: on a map, 1 inch represents 28 miles. how many b inches would be necessary to represent a distance of 383.6 miles ?
Options: a. 5.2, b. 7.4, c. 13.7, d. 21.2, e. 28.7

Ex Output:
c