Question 935222
The unknown variable is the side length of the congruent squares to cut.  You want to derive a formula for the area of the box.


The flaps folded upward will be the height of the box.  Let the side of each square to cut be length x.  This makes height x also.


The area of just the bottom of the box is {{{(10-2x)^2}}}.  The four box sides will also be congruent, and are of area  x(10-2x).


Total area of this box is  {{{highlight_green((10-2x)^2+4(x(10-2x)))}}}; and just needs to be simplified to finish it.