Question

a 24 kg rock containing 3,528 j of potential energy rests upon the edge of a cliff how tall is the cliff

Answer 1

Potential gravitational energy is computed with the formula:

$PEgrav=mgh$

Where:
PEgrav = Potential gravitation energy (J)
m = mass (kg)
h = height (m)
g = acceleration due to gravity (9.8m/s^2) 

Take note that acceleration due to gravity is a constant. 

All you need to do is put in what you know and solve for what you don't know. So your given is the following:
PEgrav = 3,528J
m = 24 kg
g = 9.8 m/s^2
Put that into your formula:
$PEgrav=mgh$
$3,528J = (24kg)(9.8m/s^{2})(h)$
$3,528J = (235.2kg.m/s^{2})(h)$
$\frac{3,528J}{235.2kg.m/s^{2}} = h$
$15m=h$

The height of the cliff is 15m.