Car a began a journey from a point at 9 am, traveling at 30 mph. at 10 am car b started traveling from the same point at 40 mph in the same direction as car a. at what time will car b pass car a?

Let after t hours the distances D1 traveled by car A

=> D1 = 30 t

Car B starts at 10 am and will, therefore, have spent one hour less than car A when it passes it.

After (t - 1) hours, distance D2 traveled by car B 

=> D2 = 40 (t - 1)

When car B passes car A, they are at the same distance from the starting point and therefore D1 = D2 

=> 30 t = 40 (t - 1)

Solve the equation for t,

=> 30 t = 40t - 40

=> 10 t = 40

=> t = 4

=> Car B passes car A at = 9 + 4 = 13 pm.