We can first obtain time of flight from vertical fall
Initial velocity U=0, d = 6 m, a = 9.8 m/s²
d = ut + 1/2 at²
6.0 = 0 + (1/2 × 9.80 t²)
t = √(12/9.8)
= 1.106 sec
Horizontal velocity = Vh = Dh/t
= 24.0 /1.106 s
= 21.69 m/s
The ball was thrown at a speed of 21.69 m/s