Answer:
The box is a cuboid. The longest to fit in will be kept diagonally. So we will find the diagonal of the cuboid.
[tex]Diagonal = \sqrt{L^{2}+ B^{2}+ H^{2} } = \sqrt{20^2+ 12^2+6^2 }=\sqrt{400+144+36}\\[/tex]
[tex]\sqrt{580} = 24.08 =24inch[/tex]
