Which expression represents the volume of the box in terms of x?

The volume formula for any 4 sided figure is V = l*w*h.  If you have a side length measuring 27, and you cut out 2 corners measuring x, your side length measure is (27-2x).  If you have a width measure of 18 and you cut out 2 corners measuring x, your width measure is (18-2x).  If you fold up each of those cut out corners, you get the height.  That height is what we cut away, "x". So the volume will be represented by (27-2x)(18-2x)(x)