#### Answer

The solutions are $\sqrt{71} $and $-\sqrt{71}.$

#### Work Step by Step

$-3w^{2}=-213\qquad$ ...divide each side with $-3$
$ w^{2}=71\qquad$ ...take square roots of each side.
$\sqrt{w^{2}}=\sqrt{71}\qquad$ ...simplify
...When solving an equation of the form $x^{2}=s$ where $s>0$,
we find both the positive and negative solutions.
$ w=\pm\sqrt{71}\qquad$ ...we cannot simplify any further.