The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 6.6392\\[1 em]x_2 &= -3.8196+6.1748i\\[1 em]x_3 &= -3.8196-6.1748i \end{aligned} $$Polynomial $ x^3+x^2+2x-350 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.