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: if a lends rs. 3150 to b at 8 % per annum and b lends the same sum to c at 12.5 % per annum then the gain of b in a period of 2 years is ?
Options: a. 280, b. 295, c. 283.5, d. 245, e. 200
[EX A]: c

[EX Q]: Problem: what is the tens digit of 6 ^ 10 ?
Options: a. 7, b. 3, c. 5, d. 1, e. 9
[EX A]: a

[EX Q]: Problem: 3 positive integers a, b, and c are such that their average is 20 and a ≤ b ≤ c. if the median is ( a + 13 ), what is the least possible value of c ?
Options: a. 21, b. 22, c. 23, d. 24, e. 25
[EX A]:
e