The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 4+i\\[1 em]x_2 &= 4-i\\[1 em]x_3 &= 4+i\\[1 em]x_4 &= 4-i \end{aligned} $$Polynomial $ x^4-16x^3+98x^2-272x+289 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.