A scuba diver dove from the surface of the ocean to an elevation of −89 9
10
feet at a rate of −18 feet per minute. After spending 11.75 minutes at that elevation, the diver ascended to an elevation of −38
9
10
feet. The total time for the dive so far was 18
1
8
minutes. What was the rate of change in the diver's elevation during the ascent? Round your answer to the nearest hundredth.

The rate of change of the diver's elevation was
ft/min.