SPEED is
        (distance covered) / (time to cover the distance) .
The car's average SPEED is
               (100 km) / (15min)
           =    6-2/3 km per minute.
VELOCITY is Â
       (distance and direction between start-point and end-point)
divided by
       (time to travel from start-point to end-point).
The car ended up at the starting point, so the distance between
stating-point and end-point is zero.
   Velocity = (zero) / (time to travel from start-point to end-point)
           = Zero .
