Task: Question Answering
Input (English): 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 (English): a