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: 50 % of a number is more than 40 % of 120 by 180. find the number ?
Options: a. 456, b. 480, c. 420, d. 445, e. 320
Example Output: a

Example Input: Problem: you have been given a physical balance and 7 weights of 40, 42, 36, 33, 47, 52 and 67 kgs. keeping weights on one pan and object on the other, what is the maximum you can weigh less than 169 kgs.
Options: a. 163, b. 166, c. 162, d. 164, e. 165
Example Output: e

Example Input: Problem: how much time does a train 160 metres long running at 72 km / hr take to pass a pole ?
Options: a. 8 s, b. 2.5 s, c. 7.5 s, d. 7.6 s, e. 7.4 s
Example Output:
a