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 the area of a circle decreases by 66 %, then the radius of a circle decreases by
Options: a. 20 %, b. 18 %, c. 36 %, d. 64 %, e. none of these
[EX A]: e

[EX Q]: Problem: what is the greatest positive integer n such that 3 ^ n is a factor of 36 ^ 100 ?
Options: a. 100, b. 200, c. 300, d. 600, e. 900
[EX A]: b

[EX Q]: Problem: two pipes a and b can fill a tank in 20 and 30 minutes respectively. if both the pipes are used together, then how long it will take to fill the tank ?
Options: a. 10 mins, b. 12 mins, c. 15 mins, d. 20 mins, e. 30 mins
[EX A]:
b