To solve this problem we will directly use the formula:
..........Equation 1
where symbols have their usual meanings.
Here g=32.2 ft/s^2 and h=108 feet
Therefore, from Equation 1 we will get:
....Equation 2
Plugging in the values in Equation 2 we get:
seconds.
Therefore, the amount of time it would have taken the rock to fall is 2.59 seconds.