As the ball is "thrown vertically down from the edge" of the cliff, the distance fallen will be the height of the cliff.
Let's use the formula s = u t + frac(1)(2) a t^(2)s=ut+12at2; where ss is the distance, uu is the initial velocity, aa is the acceleration, and tt is the time taken.
In this case, aa will be equal to 9.819.81 "m/s"^(2)m/s2, which is the acceleration due to gravity:
Rightarrow s = 0⇒s=0 "m/s"m/s times 6×6 "s"s + frac(1)(2) times 9.81+12×9.81 "m/s"^(2) times 6^(2)m/s2×62 "s"^(2)s2
Rightarrow s = 4.905⇒s=4.905 "m/s"^(2) times 36m/s2×36 "s"^(2)s2
therefore s = 176.58 "m"
Therefore, the cliff is around 177 "m" high.