$q=-6x^{3}$

$x=-\frac{6^{\frac{2}{3}}\sqrt[3]{q}}{6}$
$x=\frac{6^{\frac{2}{3}}e^{\frac{\pi i}{3}}\sqrt[3]{q}}{6}$
$x=\frac{6^{\frac{2}{3}}e^{\frac{5\pi i}{3}}\sqrt[3]{q}}{6}$

$x=-\frac{6^{\frac{2}{3}}\sqrt[3]{q}}{6}$