Answer:
The light intensity at a depth of 24 feet is 3.0143 lumens.
The light intensity will be 7 lumenus at the depth of 9.3732 feet approximately.
Explanation:
Consider the provided formula.

Where I is the intensity of light and x is the depth.
Part (A) Find the light intensity at a depth of 24 feet.
Substitute x=24 in above formula.





Hence, the light intensity at a depth of 24 feet is 3.0143 lumens.
Part (B) At what depth is the light intensity 7 lumens
Substitute I=7 in above formula.





Hence, the light intensity will be 7 lumenus at the depth of 9.3732 feet approximately.