Two boys come out to meet each other from points A and B at a speed of 5 km/h each.
The distance between A and B is 10 km.
At the same time, a dog runs out from point A to point B at a speed of 10 km/h. The dog runs to the second boy, turns around, and then runs to the first boy, and so on.
How far will the dog run before the boys meet if the dog needs X time to turn around.