The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -2+\frac{ 2 }{ 3 }i\\[1 em]x_2 &= -2-\frac{ 2 }{ 3 }i \end{aligned} $$The solutions of $ 9x^2+36x+40 = 0 $ are: $ x = -2+\dfrac{ 2 }{ 3 }i ~ \text{and} ~ x = -2-\dfrac{ 2 }{ 3 }i$.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this quadratic equation.