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: 30 pens and 75 pencils were purchased for 750. if the average price of a pencil was 2.00, find the average price of a pen.
Options: a. 20, b. 11, c. 12, d. 13, e. 14
Example Output: a

Example Input: Problem: x does a work in 20 days. y does the same work in 40 days. in how many days they together will do the same work ?
Options: a. 10, b. 12, c. 20, d. 30, e. 13.33
Example Output: e

Example Input: Problem: a palindrome is a number that reads the same forward and backward, such as 196. how many odd, 4 - digit numbers are palindromes ?
Options: a. 40, b. 45, c. 50, d. 90, e. 2500
Example Output:
d