We just want to make sure we know what our units are doing. I haven't written the units here to save some space. But we get 1 over 500 times dh dt. So if we want to solve for dh dt, you can multiply both sides by 500. And you get the rate at which our height is changing is equal to 500 times secant squared of pi over 4. That is 1 over cosine squared of pi over 4. Cosine of pi over 4.