Answer:
16/3 feet/second
Explanation:
The elevator starts 120 feet below ground level and after 15 seconds the elevalor is at 40 feet below ground level.
The distance travelled in 15 seconds = 120-40=80 feet.
So, the change in elevation is 15 seconds is 80 feet.
As the rate of change of elevation is the chanve of elevation in unit time
=16/3 feet/second
=5.33 feet/ second