How is this changing with respect to time? So we can just rewrite this, just so it gets a little bit cleaner. Let me rewrite everything I've done. 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.