So we've got dv, the rate at which our volume is changing with respect to time. The rate at which our volume is changing with respect to time is equal to pi over 12 times 3h of t squared. Or I could just write that as 3h squared. Times the rate at which the height is changing with respect to time. Times dh dt. And you might be a little confused. You might have been tempted to take the derivative over here with respect to h. But remember, we're thinking about how things are changing with respect to time.