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: bill made a profit of 10 % by selling a product. if he had purchased that product for 10 % less and sold it at a profit of 30 %, he would have received $ 63 more. what was his original selling price ?
Options: a. $ 850, b. $ 990, c. $ 1050, d. $ 1180, e. $ 1340
[EX A]: b

[EX Q]: Problem: by selling 15 pencils for a rupee a man loses 20 %. how many for a rupee should he sell in order to gain 20 % ?
Options: a. 8, b. 7, c. 6, d. 4, e. 10
[EX A]: e

[EX Q]: Problem: a certain fraction is equivalent to 2 / 5. if the numerator of the fraction is increased by 4 and the denominator is doubled, the new fraction is equivalent to 1 / 4. what is the difference of the numerator and denominator of the original fraction ?
Options: a. 49, b. 35, c. 28, d. 24, e. 21
[EX A]:
d