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: an aeroplane covers a certain distance at a speed of 150 kmph in 2 hours. to cover the same distance in 1 2 / 3 hours, it must travel at a speed of :
Options: a. 1300 kmph, b. 160 kmph, c. 180 kmph, d. 1080 kmph, e. none
Example Output: c

Example Input: Problem: a person ' s present age is two - fifth of the age of his mother. after 8 years, he will be one - half of the age of his mother. how old is the mother at present
Options: a. 38, b. 40, c. 42, d. 44, e. 45
Example Output: b

Example Input: Problem: a retail appliance store priced a video recorder at 20 percent above the wholesale cost of $ 200. if a store employee applied the 10 percent employee discount to the retail price to buy the recorder, how much did the employee pay for the recorder ?
Options: a. $ 198, b. $ 216, c. $ 220, d. $ 230, e. $ 240
Example Output:
b