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: the least number which when divided by 5, 6, 7 and 8 leaves a remainder 3, but when divided by 9 leaves no remainder, is :
Options: a. 2377, b. 1683, c. 2677, d. 9972, e. 1611

Ex Output:
b

Ex Input:
Problem: the product x of two prime numbers is between 17 and 60. if one of the prime numbers is greater than 2 but less than 6 and the other is greater than 13 but less than 25, then x =
Options: a. 18, b. 29, c. 37, d. 44, e. 57

Ex Output:
e

Ex Input:
Problem: a man sitting in a train which is travelling at 64 kmph observes that a goods train travelling in a opposite direction, takes 18 seconds to pass him. if the goods train is 420 m long, find its speed.
Options: a. 32, b. 15, c. 18, d. 20, e. 25

Ex Output:
d