$$4+2n^3+5n\cdot3+2 = 0$$
Answer
$$ \begin{matrix}n_1 = -0.39197 & n_2 = 0.19599+2.75957i & n_3 = 0.19599-2.75957i \end{matrix} $$
Explanation
$$ \begin{aligned} 4+2n^3+5n\cdot3+2 &= 0&& \text{simplify left side} \\[1 em]4+2n^3+15n+2 &= 0&& \\[1 em]2n^3+15n+6 &= 0&& \\[1 em] \end{aligned} $$
This polynomial has no rational roots that can be found using Rational Root Test.
Roots were found using qubic formulas.
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Polynomial Equations Solver