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 270 metres long bullet train running at the speed of 120 kmph crosses another bullet train running in opposite direction at the speed of 80 kmph in 9 seconds. what is the length of the other bullet train ?
Options: a. 226, b. 230, c. 430, d. 310, e. 260
Example Output: b

Example Input: Problem: the smallest number which when diminished by 2, is divisible by 12, 16, 18, 21 and 28 is
Options: a. 1008, b. 1010, c. 1022, d. 1032, e. 1043
Example Output: b

Example Input: Problem: the area of a square garden is q square feet and the perimeter is p feet. if q = p + 21, what is the perimeter of the garden in feet ?
Options: ['a. 24', 'b. 28', 'c. 32', 'd. 36', 'e. 40']
Example Output:
b