And just so that the next few things I do will appear a little bit clearer, we're assuming that height is a function of time. In fact, it's definitely a function of time. As time goes on, the height will change because we're pouring more and more water here. So instead of just writing h to the third power, which I could write over here, let me write h of t to the third power, just to make it clear that this is a function of t. h of t to the third power. Now, what is the derivative with respect to t of h of t to the third power? Now, you might be getting a tingling feeling that the chain rule might be applicable here. So let's think about the chain rule.