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 can do a piece of work in 4 hours; b and c together can do it in 3 hours, while a and c together can do it 2 hours. how long will b alone take to do it ?
Options: a. 8 hours, b. 10 hours, c. 12 hours, d. 24 hours, e. none of these

Ex Output:
c


Ex Input:
Problem: at the wholesale store you can buy an 8 - pack of hot dogs for $ 1.55, a 20 - pack for $ 3.05, and a 250 - pack for $ 22.95. what is the greatest number of hot dogs you can buy at this store with $ 205 ?
Options: a. 1,108, b. 2,100, c. 2,140, d. 2,124, e. 2,256

Ex Output:
c


Ex Input:
Problem: the sum of the present ages of a father and his son is 42 years. 6 years ago, father ' s age was 4 times the age of the son. after 6 years, son ' s age will be :
Options: a. 14, b. 16, c. 18, d. 20, e. 22

Ex Output:

c