Write an expression for the volume in terms of x and y?

"A box with an open top is to be constructed from a square piece of cardboard, 3 ft wide, by cutting out a square from each of the four corners and bending up the sides. Let x denote the length of the side of the square being cut out. Let y denote the length of the base.

Write an expression for the volume V in terms of x and y"

First, what do they mean by " Let y denote the length of the base"? The base of what? The box of the square cardboard being used to make the box? And since the cardboard is a square, the width must be equal to lenght, so x=3, right?

The answer I got was V = (y^2)((x-y)/-2)

Apprently its wrong....

Thanks!