How do you use the remainder theorem to find which if the following is not a factor of the polynomial x^3-5x^2-9x+45 div x+3?

$\left(x + 3\right)$ is a factor
Little Bézout's theorem states that the remainder of dividing a polynomial ${p}_{n} \left(x\right)$ by a linear term $\left(x - a\right)$, is given by ${p}_{n} \left(a\right)$
Evaluating p_3(x)=x^3-5x²-9x+45 for $x = - 3$ we have ${p}_{3} \left(- 3\right) = 0$ then $\left(x + 3\right)$ is a factor of ${p}_{3} \left(x\right)$