Well, the volume as a function of x is going to be equal to the height, which is x, times the width, which is 20 minus two x, times the depth, which is 30 minus two x. Now what are possible values of x that give us a valid volume? Well, x can't be less than zero. You can't make a negative cut here. Somehow we would have to add cardboard or something there. So we know that x is going to be greater than or equal to zero. So let me write this down.