The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.5275\\[1 em]x_2 &= -0.5275 \end{aligned} $$The solutions of $ 3x^2-6x-4 = 0 $ are: $ x = 1-\dfrac{\sqrt{ 21 }}{ 3 } ~ \text{and} ~ x = 1+\dfrac{\sqrt{ 21 }}{ 3 }$.
You can use step-by-step quadratic equation solver to see a detailed explanation on how to solve this quadratic equation.