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 can do a piece of work in 4 hours; b and c together can do it in 3 hours, while a and c together can do it 2 hours. how long will b alone take to do it ?
Options: a. 8 hours, b. 10 hours, c. 12 hours, d. 24 hours, e. none of these
Example Output: c

Example Input: Problem: the total age of a and b is 12 year more than the total age of b and c. c is how many years younger than a ?
Options: a. 12, b. 24, c. data inadequate, d. none of these, e. 34
Example Output: a

Example Input: Problem: there are 20 cm, 21 cm, 22 cm, 23 cm, 24 cm, 25 cm rods of quantities 23, 64, 32 respectively. find average of this data.
Options: a. 32.25, b. 21.45, c. 45, d. 22.45, e. 22
Example Output:
d