The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 2.5198\\[1 em]x_2 &= -1.2599+2.1823i\\[1 em]x_3 &= -1.2599-2.1823i \end{aligned} $$Polynomial $ 3x^3-48 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.