Calculate 3(2 1/5 miles) + 1(1.5 miles) (I don't think you really meant "11.5 miles).
6 3/5 + 1.5 = 6.6 + 1.5 = 8.1 miles.
Looking again at your post, I'm wondering whether your "1 1.5 miles" was supposed to mean "1 1/5 miles."
If so, the correct answer is different from the first one:
3(2 1/5 miles) + 1(1 1/5 miles) = 6 3/5 miles + 1 1/5 miles = 7 4/5 miles.
