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?
Choose the correct choice from the following
A) 9% B) 10% C) 11% D) 12% E) 15%
Let x be the discount on Pony jeans. Then 0.22-x is the discount on Fox jeans.   3(0.22-x)(15) + 2x(18) = 8.91   9.9 - 45x + 36x = 8.91   9x = 0.99   x = 0.11   The answer is 11%.
<result>C</result>
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?