Question 1082919
v for the volume:
x, the size of edge length of the cutout corner


{{{v=x(12-2x)(12-2x)}}}
-
{{{v=x(144-48x+4x^2)}}}
{{{v=4x^3-48x^2+144x}}}



{{{dv/dx=12x^2-96x+144=0}}}
{{{3x^2-24x+36=0}}}


discriminant,  {{{24^2-4*3*36=144=12^2}}}


{{{x=(24+- 12)/6}}}

{{{system(cross(x=6),or,highlight(x=2))}}}


Length and width each is  8 inches.
Volume is 128 cubic inches.