Up Hill and Down Hill

A Classic Puzzle by Lewis Carroll
Two travelers spend from 3 o'clock till 9 in walking along a level road, up a hill, and back home again: their pace on the level being 4 miles an hour, up hill 3, and down hill 6.
Find the distance walked: also (within half an hour) the time of reaching the top of the hill

12 miles each way, finished within 1/2 hour of 18:30 (6:30)?