First of all let's notice that while our original polynomial is real. So we can rule out the even options B and D. At this point, if the polynomial has a factor of it means tha is a zero of the polynomial. Let's check both 2 (for option a) and -2 (for option c)
At this point 2 is a zero, and our final factoring is a
The are of a square is determined by squaring the side. And the length will hence, be determined by square rooting the area. ∴ length of this square is = √84 = 9.165