Answer:
2⅓ feet per second.
Step-by-step explanation:
10 seconds after he entered the water, the depth of the diver = 30 feet
40 seconds after he entered the water, the depth of the diver = 100 feet
The scuba diver's average rate of change

The scuba diver's average rate of change is 2⅓ feet per second.
In the context of this scenario, it means the scuba diver descends a depth of 2⅓ feet every second.