Ball is projected upwards with speed 20 m/s
now using kinematics
[tex]v_f^2 - v_i^2 = 2 a\delta x[/tex]
here when ball returns back to same position.
total displacement of ball will be zero.
[tex]v_f^2 - v_i^2 = 0[/tex]
[tex]vf = vi[/tex]
So ball will return to initial position with same speed in opposite direction.