a scuba diver dove from the surface of the ocean to an elevation of -79 9/10 feet at a rate of -18.8 feet per minute, After spending 12.75 minutes at that elevation, the diver ascended to an elevation of -28 9/10 feet. The total time for the dive so far was 19 1/8 minutes. what was the rate of change in the diver's elevation during the ascent?