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.

Example Input: Problem: buses a and b start from a common bus stop x. bus a begins to travel in a straight line away from bus b at a constant rate of 30 miles per hour. one hour later, bus b begins to travel in a straight line in the exact opposite direction at a constant rate of 50 miles per hour. if both buses travel indefinitely, what is the positive difference, in minutes, between the amount of time it takes bus b to cover the exact distance that bus a has covered and the amount of time it takes bus b to cover twice the distance that bus a has covered ?
Options: a. 36, b. 84, c. 132, d. 144, e. 180
Example Output: b

Example Input: Problem: find large number from below question the difference of two numbers is 1000. on dividing the larger number by the smaller, we get 10 as quotient and the 10 as remainder
Options: a. 1234, b. 1110, c. 1456, d. 1200, e. 1600
Example Output: b

Example Input: Problem: a man rows his boat 110 km downstream and 90 km upstream, taking 3 hours each time. find the speed of the stream ?
Options: a. 6, b. 5, c. 7.5, d. 3.5, e. 2.5
Example Output:
d