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 man ' s speed with the current is 18 km / hr and the speed of the current is 2.5 km / hr. the man ' s speed against the current is ?
Options: a. 10, b. 18, c. 50, d. 30, e. 40
Example Output: b

Example Input: Problem: a person buys an article at $ 600. at what price should he sell the article so as to make a profit of 8 % ?
Options: a. 670, b. 689, c. 648, d. 740, e. 889
Example Output: c

Example Input: Problem: if the sides of a rectangle are increased by 35 %, what is the percentage increase in the area ?
Options: a. 38.25 %, b. 40.25 %, c. 82.25 %, d. 50 %, e. 65 %
Example Output:
c