How do I find time?

Answer: 3
H = 45 m ,
time required for the stone
S = u.t+(1/2) g.t²
45 = (1/2) 9.81. t² since u( initial velocity) = 0 ; S =H.
t² = 9.17 s
t = 3.02 s
therefore answer is 3 m/s
if you satisfy with explanation, please give brainiest ;