Answer
$$y=1+\sqrt{7},\:y=1-\sqrt{7}$$
Work Step by Step
The quadratic formula states:
$$x_{1,\:2}=\frac{-b\pm \sqrt{b^2-4ac}}{2a}$$
Thus, solving the equation, we find:
$$ y_{1,\:2}=\frac{-\left(-6\right)\pm \sqrt{\left(-6\right)^2-4\cdot \:3\left(-18\right)}}{2\cdot \:3} \\ y=1+\sqrt{7},\:y=1-\sqrt{7}$$