The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= -0.1452+0.6751i\\[1 em]x_2 &= -0.1452-0.6751i\\[1 em]x_3 &= -0.4094+0.358i\\[1 em]x_4 &= -0.4094-0.358i\\[1 em]x_5 &= 0.6974+0.7256i\\[1 em]x_6 &= 0.6974-0.7256i \end{aligned} $$Polynomial $ 42x^6-12x^5+20x^4+8x^3+21x^2+12x+6 $ has no rational roots that can be found using Rational Root Test, so the roots were found using Newton method.