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: two trains are moving in opposite directions at 60 km / hr and 90 km / hr. their lengths are 1.15 km and 0.6 km respectively. the time taken by the slower train to cross the faster train in seconds is ?
Options: a. 42, b. 9, c. 7, d. 67, e. 15
Example Output: a

Example Input: Problem: a cricket player whose bowling average was 23.50 runs per wicket, takes 5 wicket for 52 runs in a match. due to this his average decreases by 0.50. what will be the number of wickets taken by him till the last match ?
Options: a. 64, b. 72, c. 131, d. 456, e. 108
Example Output: c

Example Input: Problem: sakshi can do a piece of work in 12 days. tanya is 20 % more efficient than sakshi. the number of days taken by tanya to do the same piece of work is ?
Options: a. 10, b. 12, c. 14, d. 16, e. 18
Example Output:
a