What are the dimensions of an open top rectangular box from an 18 by 12 board

Question

Dimensions for a rectangular box with 18 by 12 board

Answer 1

I don't have a formula for this, but, here's a seat of the pants solution, I think:

 

You need five sides, bc the box is open topped.

 

So, if you cut off 1.5 inches by 12 inches four times,

 

Then you'd have a 12 by 12 piece left for the bottom.  Each side would be 1.5 by 12.