You will be given a definition of a task first, then some input of the task.
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.

Problem: working alone, mary can pave a driveway in 4 hours and hillary can pave the same driveway in 3 hours. when they work together, mary thrives on teamwork so her rate increases by 33.33 %, but hillary becomes distracted and her rate decreases by 50 %. if they both work together, how many hours will it take to pave the driveway ?
Options: a. 2 hours, b. 4 hours, c. 5 hours, d. 6 hours, e. 7 hours
Output:
a