The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.5858\\[1 em]x_2 &= -3.4142\\[1 em]x_3 &= -1.2+0.4i\\[1 em]x_4 &= -1.2-0.4i \end{aligned} $$Polynomial $ 5x^4+32x^3+66x^2+56x+16 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.