Understand the volume of a rectangle equals its length x width x height. Volume height width depth. So to answer the question we want to maximise the function.
This is the volume of the rectangular shaped box which corresponds to the dimensions entered for length width and height.
The volume of a rectangular box can be calculated if you know its three dimensions. To that add twice the product W x D. It is bounded by six faces three of which meet at its vertices and all of which are perpendicular to their respective adjacent faces. The volume formula for a rectangular box is height x width x length as seen in the figure below.