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.

[EX Q]: Problem: how many prime numbers are between 76 / 8 and 124 / 5 ?
Options: a. 1, b. 2, c. 3, d. 4, e. 5
[EX A]: e

[EX Q]: Problem: if the price of a certain computer increased 30 percent from b dollars to 351 dollars, then 2 b =
Options: a. 540, b. 570, c. 619, d. 649, e. 700
[EX A]: a

[EX Q]: 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 $ 9 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 discounts rates is 22 percent, what is the discount rate on pony jeans ?
Options: a. 9 %, b. 10 %, c. 11 %, d. 12 %, e. 13 %
[EX A]:
b