Answer :

dln
Δx=Vi(t)+.5at²
Δx=80
a=9.8
Vi=0 since its from rest, the initial velocity is 0.
80=0+.5(9.8)t²
t=16.33
You can use one of the big five equations: Vf=Vi+at
Vf=0+9.8(16.33)
Vf=160.034 m/s