Begin by taking out -3 as a common factor.
-3(x^3 - 2x^2 - 2x - 3)
If x + 3 is a factor, what is inside the brackets should be 0 when x = - 3 It is not. There is only one real root and that is when (x - 3) is equated to 0. Just to show the root is +3, the graph is included.