a scuba diver dove from the surface of the ocean to an elevation of -99 9/10 feet at a rate of -20 feet per minute. after spending 14.25 minutes at that elevation, the diver ascended to an elevation of -19 9/10 feet. the total time for the dive so far was 21 1/8 minutes. what was the rate of change in the diver's elevation during the ascent? tound your answer to the nerest hundredth.