The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.9129\\[1 em]x_2 &= -0.9565+1.6567i\\[1 em]x_3 &= -0.9565-1.6567i \end{aligned} $$Polynomial $ x^3-7 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.