How do you complete the square to solve -3x^2-18x-25= 0?

$f \left(x\right) = - 3 \left({x}^{2} + 6 x + 9\right) + 27 - 25 = 0$
${\left(x + 3\right)}^{2} = \frac{- 2}{- 3} = \frac{2}{3}$ --> $\left(x + 3\right) = \pm \frac{\sqrt{2}}{\sqrt{3}} = \pm \frac{\sqrt{6}}{3}$
$x = - 3 \pm \frac{\sqrt{6}}{3}$