If the coefficients of $x^{−2}$ and $x^{−4}$ in the expansion of $\begin{align*} \begin{bmatrix}x^{\frac{1}{3}}+ \frac{1}{2x^{\frac{1}{3}}} \end{bmatrix}^{18}, (x>0) \end{align*}$ are $m$ and $n$ respectively, then $\frac{m}{n}$ is equal to :

Question

$\begin{array}(1)\; 182 \\ (2)\; \frac{4}{5} \\ (3)\; \frac{5}{4} \\ (4)\; 27 \end{array}$