Well, we can view this, as I said a few seconds ago, we can view this as a composite function. What do we do first with our x? Well, we do all of this business. And we could call this u of x. And then, whatever we get for u of x, we raise that to the 4th power. So the way that we would take the derivative, we would take the derivative of this, you could view it as the outer function with respect to u of x, and then multiply that times the derivative of u with respect to x. So let's do that.