Assuming that the pool was drained at a constant rate, the speed at which it was drained can be expressed as a function of time. In this case, the pool level will be expressed in feet per hour.
The time changed by 4 hours (6-2), and the level of the pool changed by -8 feet (2-10). Diving the feet by the hours to get the rate of decreasing depth, we find that the rate equals -2 feet/hour.