20 how much metal is needed to smelt a cubical metal box with outer side 12 inches long if the thickness of its walls should be exactly 3 inches?

The volume of the metal box if the box was completely solid (V1), is:

V1 = (12 inches) ³

V1=1728 inches³

As there are 3 inches of metal on both sides, the widht if the metal box was not completely solid, is:

W=12 inches - (3 inchesx2)

W=6 inches

Then, the volumen of the no solid metal box is:

V2 = (6 inches) ³

V2 = 216 inches³

Therefore, the volume of metal needed to smelt the cubical metal box, is:

V3=V1-V2

V3=1728 inches³-216 inches³

V3=1512 inches³