Question 793004
<pre>
We want to start with a square piece piece of cardboard,
with dimensions x inches by x inches


{{{(matrix(17,1,

We, want, to, start, with, a, square, piece, of, cardboard,
with, dimensions, x, inches, by, x, inches))}}}{{{drawing(300,300,-6,6,-6,6, 
locate(-2,-4.2,x_inches),
rectangle(-sqrt(14)/2-3,-sqrt(14)/2-3,sqrt(14)/2+3,sqrt(14)/2+3)
  )}}}{{{(matrix(16,1,

Then, we, will, cut, squares, out, of, the, corners,
with, dimensions, 3, inches, by, 3, inches))}}}{{{drawing(300,300,-6,6,-6,6, 
locate(-4.5,-1.3,3_inches),

rectangle(-sqrt(14)/2-3,-sqrt(14)/2-3,-sqrt(14)/2,-sqrt(14)/2),
locate(-1.8,-4.25,x-6_inches),
rectangle(-sqrt(14)/2-3,sqrt(14)/2+3,-sqrt(14)/2,sqrt(14)/2),


rectangle(sqrt(14)/2,-sqrt(14)/2-3,sqrt(14)/2+3,-sqrt(14)/2),




rectangle(-sqrt(14)/2-3,-sqrt(14)/2-3,sqrt(14)/2+3,sqrt(14)/2+3),

rectangle(sqrt(14)/2,sqrt(14)/2+3,sqrt(14)/2+3,sqrt(14)/2)




  )}}}{{{(matrix(14,1,

The, reason, for, the, x-6_inches, is, because, 3,inches,are, cut,from,
both, side))}}}

{{{(matrix(7,1,

We, will,fold,up,along, the, sides))}}}{{{drawing(300,300,-6,6,-6,6, 
locate(-4.5,-1.3,3_inches),

locate(-1.8,-4.2,x-6_inches),
rectangle(-sqrt(14)/2-3,-sqrt(14)/2,-sqrt(14)/2,sqrt(14)/2),


rectangle(-sqrt(14)/2,sqrt(14)/2,sqrt(14)/2,sqrt(14)/2+3),




rectangle(sqrt(14)/2,-sqrt(14)/2,sqrt(14)/2+3,sqrt(14)/2),

rectangle(-sqrt(14)/2,-sqrt(14)/2-3,sqrt(14)/2,-sqrt(14)/2)




  )}}}{{{(matrix(11,1,

The, volume, is, found, by,V=lwh, 42=(x-6)(x-6)*3, 42=(x-6)^2*3,14=(x-6)^2,sqrt(14)=x-6,6+sqrt(14)=x))}}}

6+&#8730;<span style="text-decoration: overline">14</span> &#8776; 9.741657387 &#8776; {{{9&3/4}}} inches.

Edwin</pre>