What was the depth of the water at 4:00 P.M?

The answer to this is C. You will be able to see this based on the given illustration. Based on the unit on the vertical axis that will show that the depth increases one foot each, you also need to compute that there will be an increase of 10% from 3PM to 4PM.

It is already normal for the water levels to increase especially when there is heavy rain. It will be important for the water levels to be monitored especially if there is a chance that the water would spill or if there is a chance that there are areas that will become flooded because of the rainstorm.