I believe it should be 9(x+3)(x-3). You start by simplifying the equation so you would divide 9x^2 and -81 to get 9x^2 and -9. Next you would take the square root of both x^2 and 9 to get 3 (3 squared = 9). And then you just put 9 in front then make two separate parentheses with one be x+3 and other be x-3.
