In order to calculate the speed when the ball is 4 m above the ground, we can use Torricelli's equation:
[tex]V^2=V_0^2+2\cdot a\cdot d[/tex]Where V is the final speed, V0 is the initial speed, a is the acceleration and d is the displacement.
Using V0 = 10 m/s, a = 9.8 m/s² (gravity's acceleration) and d = 16 m (from 20 m to 4 m), we have:
[tex]\begin{gathered} V^2=10^2+2\cdot9.8\cdot16\\ \\ V^2=100+313.6\\ \\ V^2=413.6\\ \\ V=20.34\text{ m/s} \end{gathered}[/tex]Therefore the final speed is 20.34 m/s.
