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: the speed of a boat in still water is 15 km / hr and the rate of current is 3 km / hr. the distance travelled downstream in 24 minutes is
Options: a. 17.2 km, b. 7.2 km, c. 7.6 km, d. 17.6 km, e. 27.2 km
Example Output: b

Example Input: Problem: exactly 35 % of the reporters for a certain wire service cover local politics in country x. if 30 % of the reporters who cover politics for the wire service do not cover local politics in country x, what percent of the reporters for the wire service do not cover politics ?
Options: a. 20 %, b. 42 %, c. 44 %, d. 50 %, e. 84 %
Example Output: d

Example Input: Problem: by selling an article for $ 195, a person gains $ 45. what is the gain % ?
Options: a. 25 %, b. 30 %, c. 50 %, d. 20 %, e. 10 %
Example Output:
b