Answer
$\overline{x}=0, \overline{y}=1$
Work Step by Step
The triangle with vertices $(-1,0), (1,0), (0,3)$ is symmetric about the $y-axis$ .This implies that the center of mass has $x$-coordinate of $0$.
Also, the y-coordinate is a third of the distance of $(0,3)$
This means that $\overline{x}=0$ and $\overline{y}=\dfrac{3}{3}=1$
