Leona throws a baseball 10.0m [e] to her teammate nikki. nikki throws it back to leona. the entire flight of the ball took 5.5s. what is the average velocity of the ball?

Velocity = (total displacement) / (time of travel)
                  in the direction from start to finish.

Displacement = (distance between the start-point and end-point,
                           regardless of the route traveled from start to finish)
                           in the direction from start to finish.

The ball started with Leona and ended with Leona.
Displacement is zero.

Average velocity = (zero) / (5.5 s)  =  zero .