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.

[EX Q]: Problem: for each color copy, print shop x charges $ 1.20 and print shop y charges $ 1.70. how much greater is the charge for 40 color copies at print shop y than at print shop x ?
Options: a. $ 14, b. $ 16, c. $ 18, d. $ 20, e. $ 22
[EX A]: d

[EX Q]: Problem: a, b, c can complete a piece of work in 24, 8,12 days. working together, they complete the same work in how many days ?
Options: a. 4, b. 4 / 5, c. 7 / 9, d. 10, e. 24 / 7
[EX A]: a

[EX Q]: Problem: after replacing an old member by a new member, it was found that the average age of 5 members of a club is the same as it was 3 years ago. what is the difference between the ages of the replaced and the new member ?
Options: a. 12, b. 13, c. 14, d. 15, e. 16
[EX A]:
d