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: when x is multiplied by 3, the result is 10 more than the result of subtracting x from 26. what is the value of x ?
Options: a. - 4, b. 9, c. 11, d. 13, e. 22
Example Output: b

Example Input: Problem: the cash difference between the selling prices of an book at a profit of 12 % and 20 % is $ 3. the ratio of the two selling prices is :
Options: a. 55: 23, b. 52: 33, c. 52: 53, d. 45: 53, e. 14: 15
Example Output:
e