Although I think...  the average velocity means, total distance over total time  so consider the formula speed=distance/time.  And break it down, the first part:  speed=40 km/h, time 2 h  distance= speed *times* time  = 40 * 2  = 80 km  Then the second part:  speed=60 km/h, time 2 h  distance= speed *times* time  = 60 * 2  = 120 km  Total distance / Total time = Average Velocity (keep in mind the basic formula speed=distance/time)  therefore, (120+80) km / 4 hrs  = 50 km/h  Hope I helped :)

so consider the formula speed=distance/time.  And break it down, the first part:  speed=40 km/h, time 2 h  distance= speed *times* time  = 40 * 2  = 80 km