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 10 days, 25 men left the fort. find out the number of days for which the remaining food will last.
Options: a. 44, b. 42, c. 40, d. 38, e. 36
Example Output: b

Example Input: Problem: a merchant marks his goods up by 30 % and then offers a discount of 10 % on the marked price. what % profit does the merchant make after the discount ?
Options: a. 17 %, b. 25 %, c. 69 %, d. 31 %, e. 19 %
Example Output: a

Example Input: Problem: in what time will a train 100 metres long cross an electric pole, if its speed be 144 km / hr ?
Options: a. 2.5 sec, b. 4.25 sec, c. 5 sec, d. 12.5 sec, e. none
Example Output:
a