*how*to solve it, not the actual answer. Here's the question:

A stone is dropped from a sea cliff and the sound of it hitting the ocean is heard 3.4s after it's release. If the speed of sound is 340 m/s, how high is the cliff.

Basically, I know the distance down, and the distance back up again are the same, and the the acceleration of the rock is -9.8m/s/s (gravity). I've tried setting the distances equal to each other, then plugging in the numbers to get the time it takes the sound to travel the distance, then multiply that number by 340m/s to get the distance, but alas that hasn't worked.

I'm sort of at a loss as to what I should do...