We need first to remember the formula to solve quadratic equations
then we can see from the question that the constants will be a=3, b=3 and c=-18, then replacing this values in the formula we obtain
[tex]x=\frac{-3\pm\sqrt[]{9-4(3)(-18)}}{2(3)}=\frac{-3\pm\sqrt[]{9+216}}{6}=\frac{-3\pm\sqrt[]{225}}{6}=\frac{-3\pm15}{6}[/tex]then the two solutions will be
[tex]x=\frac{-3-15}{6}=-3[/tex]and
[tex]x=\frac{-3+15}{6}=\frac{12}{6}=2[/tex]
