This is dv dt. And this is going to be equal to, well, we could take the constants out of this. This is going to be equal to pi over 12 times the derivative with respect to t of h to the third power. 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.