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 n is a positive integer and n ^ 2 is divisible by 36, then the largest positive integer that must divide n is
Options: a. 6, b. 12, c. 24, d. 36, e. 48
[EX A]: a

[EX Q]: Problem: find the simple interest on rs. 72,000 at 16 2 / 3 % per year for 9 months.
Options: a. 7500, b. 6500, c. 9000, d. 9500, e. none of them
[EX A]: c

[EX Q]: Problem: a train running at the speed of 60 km / hr crosses a pole in 15 seconds. find the length of the train.
Options: a. 150 m, b. 145 m, c. 240 m, d. 135 m, e. 250 m
[EX A]:
e