The original square of piece of paper,
with the cutting and folding lines would look like this:
You see 4 congruent squares cut out of the corners.
If the length of the sides of those squares is 4 inches,
then the height of the box will be 4 inches.
Let x be the length (in inches) of the side of the square (the bottom of the box).
The surface area of the bottom (in square inches) is x^2,
and the volume of the box, calculated as area of the bottom times height,
(in cubic inches) is 4x^2
So 4x^2 = 784---> x^2 = 784/4 ---> x = sqrt 196 = 14.
Answer:
14 inches
Hope this helps :)