On a trip, a cyclist averaged 8 miles per hour for the first 12 miles and 12 miles per hour for the remaining 24 miles. If the cyclist returned immediately via the same route and took a total of 7.5 hours for the round trip, what was the average speed (in miles per hour) for the return trip?	Choose the correct option.
A) 9
B) 10
C) 11
D) 12
E) 13

Rationale: "the time to go 36 miles was 12 / 8 + 24 / 12 = 1.5 + 2 = 3.5 hours . the average speed for the return trip was 36 miles / 4 hours = 9 mph . the answer is a ."
Answer: A