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: if y > 0, ( 9 y ) / 20 + ( 3 y ) / 10 is what percent of y ?
Options: a. 40 %, b. 50 %, c. 60 %, d. 70 %, e. 75 %
Example Output: e

Example Input: Problem: a clock shows the time as 9 a. m. if the minute hand gains 7 minutes every hour, how many minutes will the clock gain by 6 p. m. ?
Options: a. 30 min, b. 35 min, c. 63 min, d. 50 min, e. 55 min
Example Output: c

Example Input: Problem: a train speeds past a pole in 25 seconds and a platform 150 m long in 30 seconds. its length is ?
Options: a. 23, b. 22, c. 21, d. 30, e. 19
Example Output:
d