Aball is thrown vertically upwards at 19.6 m/s. for its complete trip (up and back down to the starting position), its average velocity is

The average velocity of an object is given by:
Average velocity = total displacement / total time

First, we calculate the time taken to reach the maximum height of the ball. This occurs when the final velocity is 0.
Vf = Vi + at
0 = 19.6 - 9.81 * t
t = 2 seconds

The total trip will be of 4 seconds (2 seconds up, 2 seconds down)

The total displacement is given by:
s = ut + 1/2 * at²
s = 19.6 * 2 - 0.5 * 9.81 * 2²
s = 19.6 meters

This is the distance maximum height, so the total height is
19.6 * 2 = 39.2 meters

Average velocity = 39.2 / 4
Average velocity = 9.8 m/s