Definition: 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.
Input: Problem: a bookstore has a shelf that contains biographies which normally sell for $ 20 each and mysteries that normally sell for $ 12 each. during a sale, the biographies and mysteries are discounted at different rates so that a customer saves a total of $ 19 from the normal price by buying 5 discounted biographies and 3 discounted mysteries. if the sum of the discount rates for the two types of books is 30 percent, what is the discount rate on mysteries ?
Options: a. 17.18 %, b. 12 %, c. 13 %, d. 14 %, e. 15 %
Output:
a