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: a 270 metres long bullet train running at the speed of 120 kmph crosses another bullet train running in opposite direction at the speed of 80 kmph in 9 seconds. what is the length of the other bullet train ?
Options: a. 226, b. 230, c. 430, d. 310, e. 260
[EX A]: b

[EX Q]: Problem: in a mayoral election, candidate x received 1 / 2 more votes than candidate y, and candidate y received 2 / 5 fewer votes than z. if z received 25000 votes how many votes did candidate x received ?
Options: a. 18000, b. 22500, c. 24000, d. 26000, e. 32000
[EX A]: b

[EX Q]: Problem: a circular swimming pool is surrounded by a concrete wall 4 feet wide. if the area of the wall is 11 / 25 of the area of the pool, then the radius of the pool in feet is ?
Options: ['a. 22', 'b. 20', 'c. 9', 'd. 8', 'e. 1']
[EX A]:
b