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.

Example Input: Problem: a fort had provision of food for 150 men for 45 days. after 15 days, 10 men left the fort. the number of days for which the remaining food will last, is :
Options: a. 32, b. 37 1 / 4, c. 42, d. 54, e. 45
Example Output: a

Example Input: Problem: a can give b 100 meters start and c 200 meters start in a kilometer race. how much start can b give c in a kilometer race ?
Options: a. 111.12 m, b. 221.12 m, c. 271.12 m, d. 611.12 m, e. 191.12 m
Example Output: a

Example Input: Problem: a man, a woman and a boy can together complete a piece of work in 3 days. if a man alone can do it in 6 days and a women alone in 18 days, how long will a boy take to complete the work ?
Options: a. 6 days, b. 8 days, c. 9 days, d. 7 days, e. 5 days
Example Output:
c