If you were working with a flat rectangle and you were given the diagonal,
you'd want to use the Pythagorean theorem to choose two sides whose
squares would add up to the square of the diagonal.
It works exactly the same with a 3-D box. We need three dimensions for
the box, whose squares add up to the square of the diagonal between
opposite corners. That's (4)² = 16.
So (L)² + (W²) + (H²) = 16 . From there, you're completely free to pick any
numbers you want, just as long as their squares add up to 16. There are
an infinite number of possibilities. Here are a few:
1 x 1 x √14
1 x 2 x √11
2 x 2 x √8
2 x 3 x √3
1 x 3 x √6