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 5 miles per day and it will take them two days, how many miles long is the route down the mountain? Choose the correct answer:
A) 4	B) 6	C) 8	D) 12	E) 15

Rationale: "on the way down , the rate is 1.5 * 5 = 7.5 miles per day . the distance of the route down the mountain is 2 * 7.5 = 15 miles . the answer is e ."
Answer: E