We're being given a volume per time. My question to you is, right at this moment, right when we are filling our cup at 1 cubic centimeter per second, and we have exactly 2 centimeters of water in the cup, 2 centimeters deep of water in the cup, what is the rate at which the height of the water is changing? What is the rate at which this height right over here is actually changing? We know it's 2 centimeters, but how fast is it changing? Well, let's think about this a little bit. What are we being given? We're being given the rate at which the volume of the water is changing with respect to time.