Answer :
More suvat equations here, this time s=ut+1/2at^2 where s is the displacement, t is the time, and a is the acceleration.
So s=0*20+1/2*9.81*20^2
simplified: s=1/2*9.81*(20)^2
s=1962
The height of the cliff is 1962m
So s=0*20+1/2*9.81*20^2
simplified: s=1/2*9.81*(20)^2
s=1962
The height of the cliff is 1962m