Answer
$(0,3)$
Work Step by Step
By definition we have $x=r\cdot \cos(\theta)$ and $y=r\cdot \sin(\theta)$.
Here we have $r=-3 \text{ and }\theta=-90^\circ$.
Hence, after plugging these in:
$x=-3\cdot \cos(-90^\circ)=-3\cdot0=0$
$y=-3\cdot \sin(-90^\circ)=-3\cdot(-1)=3$
The point has coordinates $(0,3)$ in the rectangular coordinate system.