The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.337\\[1 em]x_2 &= -3.0587\\[1 em]x_3 &= 3.3957 \end{aligned} $$Polynomial $ 4x^3-42x-14 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.