Answer:
(x-1)(x+1)(x+3)
Explanation:
first you group the 2 parts of the equation
{(x^3) + (3x^3)} {-x - 3}
you can take out x squared from the first group and are left with x+3 and you can take out -1 from the second group also leaving you with x+3. Because these groups match it means that x+3 is a factor.
x^2(x+3) -1(x+3)
combine them
(x^2-1) (x+3)
x squared minus one can be simplified more to (x-1) and (x+1) so the final answer is (x-1)(x+1)(x+3)