A stone falls from a cliff. It lands on the ground below the cliff after 4.2 seconds. The height of the cliff can be calculated to be what?

Answer 1

It will be the distance that an object falls in 4.2 s, with zero initial vertical velocity component.

You surely know the formula for that:

Y = (g/2) t^2

t = 4.2 s g = 9.8 m/s^2