Dropping a stone.

[gapgirl1010]

A girl drops a stone into a mineshaft 122.5 m deep. How soon after she drops the stone does she hear it hit the bottom?

What formula do I use?

[alfredblase]

You are looking for the constant acceleration formulas. A quick search on google or wikipedia should provide them. Also don't forget about the period of time that sound would take to travel from the point of impact to the girl's ear. You can find the speed of sound with a google search too. =)