Since L=W, we can write the volume as ..
Assuming there is a top, the surface area is ...
If we want to minimize the surface area, we can solve the volume formula for H and sub into S.
From , ...
Sub into :
Differentiate, set to 0 and solve for L.
The width is the same. Plug this into  to find the height.
We get .
It's the same. The minimum surface area occurs when we have a cube.
That means the surface area is
Ti-83's do not do derivatives. For that get a TI-89, Voyage 200, etc.