If you were to write v of x, it would be x to the third power. So the chain rule tells us, or the chain rule is what our brain should say, hey, it becomes applicable if we're going to take the derivative of a function that can be expressed as a composite function like this. So just to be clear, we can write f of x, f of x is equal to v of u of x. I know I'm essentially saying the same thing over and over again, but I'm saying it in slightly different ways because the first time you learn this, it can be a little bit hard to grok, or really deeply understand. So I'm going to try to write it in different ways. And the chain rule tells us that if you have a situation like this, then the derivative, f prime of x, and this is something that you will see in your textbooks, so this is going to be the derivative of this whole thing with respect to u of x, so we could write that as v prime of u of x, v prime of u of x, times the derivative of u with respect to x, times u prime of x. This right over here, this is one expression of the chain rule. And so how do we evaluate it in this case?