How do you solve 18x^2+48x=-32?

Double-root: at $x = - \frac{4}{3}$
$f \left(x\right) = 9 {x}^{2} + 24 x + 16 = {\left(3 x + 4\right)}^{2} = 0$
The 2 roots are: $\pm \left(3 x + 4\right) = 0$
There is double-root at $x = - \frac{4}{3}$