If the unit for r is mph, then the distance between A and B is r miles at 1 pm. It would take 2 hours for B to catch A. At that time, both would be 3r miles away from the border if both travel on a straight line.
If the unit for r is mph, then the distance between A and B is r miles at 1 pm. It would take 2 hours for B to catch A. At that time, both would be 3r miles away from the border if both travel on a straight line.