Question 214110
The man could package the 42-inch sword in a flat box  whose dimensions are:
h = 36 inches, w = 22 inches, and depth of, say, 2 inches.
Why would this work?
Let's say that sword is placed in the flat box so that it lies along the diagonal of the box.
So with a diagonal of 42 inches, a height of 36 inches, and a width of 22 inches, we can see, from the Pythagorean theorem, that the sword would fit inside the box and the box would not exceed 36 inches in length.
{{{c^2 = a^2+b^2}}} c = the diagonal (length of the sword), a = 36 (the length of the box) and b = 22 (the width of the box).
{{{42^2 = 36^2+22^2}}}
{{{1764 = 1296+484}}}
{{{1764 = 1780}}}
The actual width of the box really need be only 21.6 inches but I rounded up the nearest inch.