Answer
It is not a factor.
Work Step by Step
The Remainder Theorem says that the remainder when a function $f(x)$ is divided by $(x-r)$ is $f(r)$.
Hence $f(-3)=4\cdot27+5\cdot9+8=161\ne0$, therefore $(x+3)$ is not a factor of $f(x)$ by the factor theorem.
The factor theorem says that if $f(c)=0$, then $(x-c)$ is a factor of $f(x)$ and vice versa.