Puzzles/Non-scientific puzzles/Boy, Girl, and a Dog

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Puzzles | Non-scientific puzzles | Boy, Girl, and a Dog

A boy, a girl, and a dog simultaneously begin movement from one point. Boy and girl are heading in one direction, boy - with speed 5 km/h, girl - 4 km/h. The dog runs from boy to girl and back with speed 10 km/h. Given that it takes no time for the dog to change direction, how much will the dog travel in 1 hour?