And then finally we have the first derivative of the height with respect to time. So you could view this as dh dt. What is this going to be? Do they give it to us? Well, look right over here. They say the height of the triangle is increasing at a rate of six meters per hour. So if they're saying h of t is increasing, they're telling us the rate of change of h of t with respect to time, so that's h prime of t, and they're telling us that it is increasing at six meters per hour.