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: in traveling from a dormitory to a certain city, a student went 1 / 3 of the way by foot, 3 / 5 of the way by bus, and the remaining 2 kilometers by car. what is the distance, in kilometers, from the dormitory to the city ?
Options: a. 30, b. 45, c. 60, d. 90, e. 120
Example Output: a

Example Input: Problem: what is the rate percent when the simple interest on rs. 810 amount to rs. 155 in 4 years ?
Options: a. 4.78, b. 4.68, c. 4.58, d. 4.48, e. 4.38
Example Output: a

Example Input: Problem: a train traveling at 72 kmph crosses a platform in 33 seconds and a man standing on the platform in 18 seconds. what is the length of the platform in meters ?
Options: a. 240 meters, b. 360 meters, c. 420 meters, d. 300 meters, e. can not be determined
Example Output:
d