Question 782693
let x be the side of square cut

then side length =
12-2x

(12-2x)^2=64

144-48x+4x^2=64

4x^2-48x+80=0

/4
x^2-12x+20=0
x^2-10x-2x+20=0
x(x-10)-2(x-10)=0
(x-10)(x-2)=0
x= 10 OR 2

x cannot be 10
so depth of box = 2inches