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: what is the value of ( 2 ) ^ - 3 ?
Options: a. 1 / 6, b. 1 / 5, c. 1 / 8, d. 1 / 9, e. 1 / 7
[EX A]: c

[EX Q]: Problem: in 10 years, a will be twice as old as b was 10 years ago. if a is now 5 years older than b the present age of b is
Options: a. 37, b. 38, c. 39, d. 35, e. 41
[EX A]: d

[EX Q]: Problem: if 5 % more is gained by selling an article for rs. 350 than by selling it for rs. 340, the cost of the article is
Options: a. 289, b. 231, c. 200, d. 288, e. 111
[EX A]:
c