The root of polynomial $ p(n) $ is:
$$ \begin{aligned}n &= -\dfrac{ 363 }{ 2 } \end{aligned} $$Step 1:
Combine like terms:
$$ \color{blue}{n} \color{blue}{-3n} -363 = \color{blue}{-2n} -363 $$Step 2:
$$ \begin{aligned} -2n-363 & = 0 \\[1 em] -2 \cdot n & = 363 \\[1 em] n & = \frac{ 363 }{ -2 } \end{aligned} $$