Answer:
-1/4 ft per second.
Explanation:
If she is 18 feet below sea level and 8 seconds later she is 20 feet, she has descended 2 feet per 8 seconds.
As we need to find feet per second, we must do 2/8 because we only have the feet per 8 seconds.
So
feet =
seconds:
2 feet / 8 seconds= 1/4 ft per second.
Therefore, she would have descended 1 feet per 4 second.
The question is asking for elevation, but this is a depression so it would be -1/4 ft per second.