I want to maximize how much it can hold. And I want to maximize it by picking my x appropriately. So let's think about what the volume of this box is as a function of x. In order to do that, we have to figure out all the dimensions of this box as a function of x. We already know that this corner right over here, which is made up of when this side and this side connect, when you fold these two flaps up, that's going to be the same height over there. That's going to be the same height over there. The height of this box is going to be x.