Question

A car is driven for 2.0 h at 40.0 km/h, then for another 2.0 at 60 km/h in the same direction

Answer 1

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 :)