Task: Question Answering
Input (English): Problem: fox jeans regularly sell for $ 15 a pair and pony jeans regularly sell for $ 18 a pair. during a sale these regular unit prices are discounted at different rates so that a total of $ 8.91 is saved by purchasing 5 pairs of jeans: 3 pairs of fox jeans and 2 pairs of pony jeans. if the sum of the two discount rates is 22 percent, what is the discount rate on pony jeans ?
Options: a. 9 %, b. 10 %, c. 11 %, d. 12 %, e. 15 %
Output (English): c