The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -1.3379\\[1 em]x_2 &= 0.419+0.9724i\\[1 em]x_3 &= 0.419-0.9724i \end{aligned} $$Step 1:
Write polynomial in descending order
$$ \begin{aligned} x^2+3+2x^3 & = 0\\[1 em] 2x^3+x^2+3 & = 0 \end{aligned} $$Step 2:
Polynomial $ 2x^3+x^2+3 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.