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: a train running at the speed of 20 km / hr crosses a post in 10 seconds. what is the length of the train ?
Options: a. 150, b. 250, c. 415, d. 200, e. 312
Example Output: d

Example Input: Problem: if a man lost 10 % by selling oranges at the rate of 12 a rupee at how many a rupee must he sell them to gain 44 % ?
Options: a. 6.5, b. 7.5, c. 7, d. 8, e. 2
Example Output: b

Example Input: Problem: a cistern 5 m long and 4 m wide contains water up to a depth of 1 m 25 cm. the total area of the wet surface is :
Options: a. 49 m 2, b. 42.5 m 2, c. 53.5 m 2, d. 55 m 2, e. 57 m 2
Example Output:
b