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 man lost 8 % by selling oranges at the rate of 25 a rupee at how many a rupee must he sell them to gain 25 % ?
Options: a. 20, b. 15, c. 18.4, d. 20, e. 12.8

Ex Output:
c

Ex Input:
Problem: if the price of a certain computer increased 30 percent from b dollars to 351 dollars, then 2 b =
Options: a. 540, b. 570, c. 619, d. 649, e. 700

Ex Output:
a

Ex Input:
Problem: working alone, mary can pave a driveway in 4 hours and hillary can pave the same driveway in 3 hours. when they work together, mary thrives on teamwork so her rate increases by 33.33 %, but hillary becomes distracted and her rate decreases by 50 %. if they both work together, how many hours will it take to pave the driveway ?
Options: a. 2 hours, b. 4 hours, c. 5 hours, d. 6 hours, e. 7 hours

Ex Output:
a