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: of the 20 members of a kitchen crew, 17 can use the meat - cutting machine, 18 can use the bread - slicing machine, and 15 can use both machines. if one member is chosen at random, what is the probability that the member chosen will be someone who can not use either machine ?
Options: a. 0, b. 1 / 10, c. 1 / 7, d. 1 / 4, e. 1 / 3
Example Output: a

Example Input: Problem: the average age of 8 men increases by 2 years when two women are included in place of two men of ages 20 and 22 years. find the average age of the women ?
Options: a. 87, b. 98, c. 30, d. 29, e. 37
Example Output: d

Example Input: Problem: before 7 years, dog a ’ s age was 4 times of dog b ’ s age and after 4 years, dog a ’ s age will be 3 times of dog b ’ s age. what is the difference of dog a ’ s age and dog b ’ s now ?
Options: a. 36, b. 42, c. 54, d. 60, e. 70
Example Output:
e