What is the height of a cliff if at 10 am the shadow is 2 feet long?
If we are to assume that the sun is on the horizon at 6 am, and directly overhead at noon, then at 10 am its angle of elevation is 4/6 * 90° = 60°
So, you have a nice 30-60-90 triangle, with the short leg (the shadow) = 2, so the long leg (the cliff) is 2√3.
Not much of a cliff.