And then they're asking us, what is h prime of negative 14? And if you're not familiar with how functions and their derivatives relate to their inverses and the derivatives of the inverse, well this will seem like a very hard thing to do. Because if you were tempted to take the inverse of f to figure out what h is, well it's tough to figure out the inverse of a third degree polynomial defined function like this. So the key, I guess, property to realize or the key truth to realize is that if f and h are inverses, then h prime of x, h prime of x, is going to be equal to, it's going to be equal to one over f prime of h of x. One over f prime of h of x. And you could now use this in order to figure out what h prime of negative 14 is. Now I know what some of you are thinking because it's exactly what I would be thinking if someone just sprung this on me, is where does this come from?