Answer:
Below in bold.
Explanation:
Speed = distance / time.
First option:
Walking at 3mph for 2 hours will give 2*3 = 6 miles.
So for 6 miles travelling at 5 mph he will take 6/5 = 1.2 hours.
Total time = 3.2 hours.
Second option:
Walking for 12 miles at 4 mph will take him 12/4 = 3 hours.
The fastest option is the second one.