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: if x + y = 260, x - y = 200, for integers of x and y, y = ?
Options: a. 200, b. 230, c. 50, d. 115, e. 150
Example Output: b

Example Input: Problem: what is the smallest integer that is multiple of 5, 711
Options: a. a. 70, b. b. 35, c. c. 385, d. d. 280, e. e. 140
Example Output: c

Example Input: Problem: a man whose speed is 8 kmph in still water rows to a certain upstream point and back to the starting point in a river which flows at 3 kmph, find his average speed for the total journey ?
Options: a. 1 kmph, b. 5 kmph, c. 6 kmph, d. 4 kmph, e. 6.8 kmph
Example Output:
e