Free falling acceleration problem?

A physics teacher stands at the edge of a cliff at Canyonlands Nation Park. The teacher wants to know how high above the base of the cliff he is, so, making sure there are no hikers below drops a large rock over the edge of the cliff. 5.8 seconds after releasing the rock, he hears the sound of the rock hitting the ground below. Using the speed of sound as 340m/s (sound travels at a constant speed), how high is the cliff?