Answer
$x=3$ is the point of relative minimum.
$x=5$ is the point of relative maximum.
Work Step by Step
$f'(x)=0$ at $x=3$ and $x=5$. Therefore, $x=3$ and $x=5$ are the points of extrema.
In the interval $(-\infty,3), f'(x)<0$ and $f'(x)>0$ in the interval $(3,5)$. Since the sign changes from $-$ to $+$ about $x=3$, it is the point of relative minimum.
Similarly, about $x=5$, $f'(x)$ changes sign from $+$ to $-$.Therefore, $x=5$ is the point of relative maximum.
