Q: 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: a group of hikers is planning a trip that will take them up a mountain using one route and back down using another route. they plan to travel down the mountain at a rate of one and a half times the rate they will use on the way up, but the time each route will take is the same. if they will go up the mountain at a rate of 6 miles per day and it will take them two days, how many miles long is the route down the mountain ?
Options: a. 16, b. 17, c. 18, d. 19, e. 20
A:
c