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 traveled from the village to the post - office at the rate of 25 kmph and walked back at the rate of 4 kmph. if the whole journey took 5 hours 48 minutes, find the distance of the post - office from the village ?
Options: a. 70 m, b. 80 km, c. 20 km, d. 10 km, e. 73 km

Ex Output:
c

Ex Input:
Problem: 11 is subtracted from 40 % of a number and results is 23. what is the number ?
Options: a. 160, b. 92, c. 88, d. 85, e. 34

Ex Output:
d

Ex Input:
Problem: two goods trains each 500 m long are running in opposite directions on parallel tracks. their speeds are 30 km / hr and 90 km / hr respectively. find the time taken by the slower train to pass the driver of the faster one ?
Options: a. 48, b. 30, c. 26, d. 23, e. 12

Ex Output:
b