Question 55078
Starting with a square piece that is x inches wide, the area is {{{x^2}}} per definition for finding the area of a square.  If the inner square is (x-3) in width, it's area is {{{(x-3)^2}}}.  So the remaining area becomes {{{x^2-(x-3)^2}}}, which expands to {{{x^2-x^2+6x-9}}}, which reduces to {{{6x-9}}}.