Girl, Boy and Dog

A girl, a boy, and a dog start walking down a road. They start at the same time, from the same point, in the same direction. The boy walks at 5 km/h, the girl at 6 km/h. The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn. How far does the dog travel in 1 hour?