Answer:
 v_average =0
Step-by-step 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