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 shop owner professes to sell his articles at certain cost price but he uses false weights with which he cheats by 12 % while buying and by 30 % while selling. what is his percentage profit ?
Options: a. 10.22 %, b. 20.22 %, c. 21.22 %, d. 60 %, e. ca n ' t be calculated
Example Output: d

Example Input: Problem: what is the greatest positive integer n such that 3 ^ n is a factor of 36 ^ 100 ?
Options: a. 100, b. 200, c. 300, d. 600, e. 900
Example Output: b

Example Input: Problem: a sum of money at simple interest amounts to rs. 720 after 2 years and to rs. 1020 after a further period of 5 years. the sum is :
Options: a. 400, b. 500, c. 600, d. 700, e. 800
Example Output:
c