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: at what rate percent per annum will a sum of money double in 6 years.
Options: a. 12.5 %, b. 13.5 %, c. 11.5 %, d. 14.5 %, e. 16.6 %
Example Output: e

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 man can row a distance of 5 km in 60 min with the help of the tide. the direction of the tide reverses with the same speed. now he travels a further 20 km in 10 hours. how much time he would have saved if the direction of tide has not changed ?
Options: a. 2, b. 8, c. 1, d. 6, e. 5
Example Output:
d