But if we want to optimize with respect to x, we have to express h as a function of x. So how can we do that? How can we express h as a function of x? Well, we know that the volume has to be 10 cubic meters. So we know that x, the width times the length times 2x times the height times h needs to be equal to 10. Or another way of saying that, this tells us that 2x squared times h needs to be equal to 10. And so if we want h as a function of x, we just divide both sides by 2x squared.