An astronaut drops a rock off the edge of a cliff on an alien moon. The distance, d(t) in meters, the rock travels after"t" seconds can be modeled by the function d(t)=-0.3(t)^2+90. How high is the cliff from the surface of the moon, and how do you know? What is the average speed, in meters per second, of the rock between 5 and 10 seconds after it was dropped?