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: if a person walks at 25 km / hr instead of 10 km / hr, he would have walked 20 km more. the actual distance traveled by him is :
Options: a. 50 km, b. 56 km, c. 13.3 km, d. 70 km, e. 80 km
Example Output: c

Example Input: Problem: the smallest number which when diminished by 2, is divisible by 12, 16, 18, 21 and 28 is
Options: a. 1008, b. 1010, c. 1022, d. 1032, e. 1043
Example Output: b

Example Input: Problem: a positive number x is multiplied by 2, and this product is then divided by 4. if the positive square root of the result of these two operations equals x, what is the value of x ?
Options: a. 9 / 4, b. 3 / 2, c. 4 / 3, d. 2 / 3, e. 1 / 2
Example Output:
a