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 and y are positive integers and 3 + x + y + xy = 17, what is the value of x + y ?
Options: a. 3, b. 5, c. 6, d. 8, e. 9
Example Output: c

Example Input: Problem: he average of 10 numbers is 23. if each number is increased by 4, what will the new average be ?
Options: a. 26, b. 27, c. 88, d. 99, e. 12
Example Output: b

Example Input: Problem: a shopkeeper buys mangoes at the rate of 7 a rupee and sells them at 5 a rupee. find his net profit or loss percent ?
Options: a. 40 %, b. 90 %, c. 33 %, d. 35 %, e. 30 %
Example Output:
a