So that's why the chain rule came into play when we were taking the derivative of h or the derivative of h of t, because we're assuming that h is a function of time. Now, what does this thing right over here get us? Well, we're telling us at the exact moment that we set up this problem, we know what dv dt is. We know that it's 1 centimeter cubed per second. We know that this right over here is 1 centimeter cubed per second. We know what our height is right at this moment. We were told it is 2 centimeters.