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.

Ex Input:
Problem: if a - b = 6 and a 2 + b 2 = 50, find the value of ab.
Options: a. a. 7, b. b. 12, c. c. 15, d. d. 18, e. e. 20

Ex Output:
a


Ex Input:
Problem: find the simple interest on rs. 72,000 at 16 2 / 3 % per year for 9 months.
Options: a. 7500, b. 6500, c. 9000, d. 9500, e. none of them

Ex Output:
c


Ex Input:
Problem: subtract. simplify your answer and write it as a proper fraction or as a whole or mixed number. 4 / 5 - 1 / 5 =
Options: a. 1 / 5, b. 2 / 5, c. 3 / 5, d. 4 / 5, e. 5 / 5

Ex Output:

c