The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 1.5874\\[1 em]x_2 &= -0.7937+1.3747i\\[1 em]x_3 &= -0.7937-1.3747i \end{aligned} $$Step 1:
Write polynomial in descending order
$$ \begin{aligned} 4-x^3 & = 0\\[1 em] -x^3+4 & = 0 \end{aligned} $$Step 2:
Polynomial $ -x^3+4 $ has no rational roots that can be found using Rational Root Test, so the roots were found using qubic formulas.