So let's rewrite volume as a function of x is equal to, and I'll write it all in yellow, so it's going to be x times, I'll multiply these two binomials first, so 20 times 30 is 600. Then I have 20 times negative two x, which is negative 40x. Then I have negative two x times 30, which is negative 60x, and then I have negative two x times negative two x, which is positive four x squared. So this part over here simplifies, and I can change the order to four x squared minus 100x plus 600. I just switched the order in which I'm writing them. So that's that, and so I can rewrite the volume of x as being equal to x times all of this business, which is, let me make sure I have enough space, let me do it a little higher, which is equal to four x to the third power minus 100x squared plus 600x. Now it'll be pretty straightforward to take the derivative.