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: sakshi can do a piece of work in 5 days. tanya is 25 % more efficient than sakshi. the number of days taken by tanya to do the same piece of work :
Options: a. 4, b. 16, c. 18, d. 25, e. 10
Example Output: a

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: of the diplomats attending a summit conference, 25 speak french, 32 do not speak russian, and 20 % of the diplomats speak neither french nor russian. if 10 % of the diplomats speak both languages, then how many diplomats attended the conference ?
Options: a. 72, b. 70, c. 108, d. 120, e. 150
Example Output:
b