A6 kg rock falls from a cliff. just before it hits the ground its speed is 24 m/s. from what height did it fall?

Rock starts out at the top of the cliff with maximum potential energy = mgh
As it falls, the potential energy decreases and kinetic energy increases.
When it hits the ground, potential energy will be zero and kinetic energy will be maximum = (1/2)mv²

Do you see that the potential energy at the top of the cliff is equal to the kinetic at the bottom?

mgh = (1/2)mv²
mass cancels out
gh = (1/2)v²
gravity, g = 9.8 m/s²
velocity, v = 24 m/s
(9.8)h = (1/2)(24)²
9.8h = 288
h = 29.3877551
round to whatever place is specified for the solution.