Let the side of the original square be x. That means the area
of the original square is x2. That means that side of
the new square would be
x + 2, so the area of the new square is (x + 2)2.
In order to get the amount of increase between the first and second square,
subtract:
x2 – (x + 2)2 = x2 – (x2
+ 4x +4) = 40
4x + 4 = 40
x + 1 = 10
x = 9 (D)