Answer:
  v_average =0
Explanation:
In kinematics the average speed defined with the distance interval traveled in a given time interval
      V = Δx /Δt
in this case the tennis ball travels a distance h to the highest point and a distance h from the highest point to the floor, so the distance you travel zero
   Dy = h -h = 0
therefore the average speed should be zero
     v_average =0