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 a lends rs. 3150 to b at 8 % per annum and b lends the same sum to c at 12.5 % per annum then the gain of b in a period of 2 years is ?
Options: a. 280, b. 295, c. 283.5, d. 245, e. 200
Example Output: c

Example Input: Problem: if 32.5 % of the 880 students at a certain college are enrolled in biology classes, how many students at the college are not enrolled in a biology class ?
Options: a. 110, b. 330, c. 550, d. 594, e. 880
Example Output: d

Example Input: Problem: one side of a rectangular field is 15 m and one of its diagonal is 18 m. find the area of the field.
Options: a. 100, b. 120, c. 150, d. 148.5, e. none
Example Output:
d