A truck drives from place a to place B at the speed of 30km / h. one hour after starting, a car also drives from place a to place B at the speed of 50km / h. it arrives at place B half an hour earlier than the truck. Find the distance between a and B

A truck drives from place a to place B at the speed of 30km / h. one hour after starting, a car also drives from place a to place B at the speed of 50km / h. it arrives at place B half an hour earlier than the truck. Find the distance between a and B

A: the distance between a and B is 112.5km