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: solution y is 30 percent liquid x and 70 percent water. if 2 kilograms of water evaporate from 6 kilograms of solution y and 2 kilograms of solution y are added to the remaining 4 kilograms of liquid, what percent of this new solution is liquid x ?
Options: a. 33 %, b. 35 1 / 2 %, c. 37 %, d. 40 %, e. 42 %

Ex Output:
d


Ex Input:
Problem: how many multiples of 4 are there between 12 and 104, inclusive ?
Options: a. 21, b. 22, c. 23, d. 24, e. 25

Ex Output:
d


Ex Input:
Problem: a certain list consists of 21 different numbers. if n is in the list and n is 6 times the average ( arithmetic mean ) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list ?
Options: a. 1 / 20, b. 1 / 6, c. 1 / 5, d. 3 / 13, e. 5 / 21

Ex Output:

d