Answer
$(3,0)$
Work Step by Step
By definition: $x=r\cdot \cos(\theta)$ and $y=r\cdot \sin(\theta)$.
Here $r=-3 \text{ and } \theta=\pi$.
Hence, after plugging these in:
$x=-3\cdot \cos(\pi)=-3\cdot(-1)=3$
$y=-3\cdot \sin(\pi)=-3\cdot0=0$
The point has coordinates $(3,0)$ in the rectangular coordinate system.