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: what will be the compound interest on a sum of rs. 20,000 after 3 years at the rate of 12 % p. a. ?
Options: a. rs. 8098.56, b. rs. 9720, c. rs. 10123.20, d. rs. 10483.20, e. none

Ex Output:
a


Ex Input:
Problem: what is the smallest positive integer x such that 66 - x is the cube of a positive integer
Options: a. 5, b. 7, c. 47, d. 9, e. 2

Ex Output:
e


Ex Input:
Problem: a start walking from a place at a uniform speed of 7 kmph in a particular direction. after half an hour, b starts from the same place and walks in the same direction as a at a uniform speed and overtakes a after 1 hour 48 minutes. find the speed of b.
Options: a. 4.7 kmph, b. 7.6 kmph, c. 4 kmph, d. 7 kmph, e. 5.3 kmph

Ex Output:

b