If the coefficients of x^-2 and x^-4 in the expansion of (x^(1/3)+1/(2 x^(1/3)))^18,(x>0), are m and n respectively, then m/n is equal to:

If the coefficients of $\displaystyle x^{-2}$ and $\displaystyle x^{-4}$ in the expansion of $\displaystyle \left(x^{\frac{1}{3}}+\frac{1}{2 x^{\frac{1}{3}}}\right)^{18},(x>0)$, are $\displaystyle m$ and $\displaystyle n$ respectively, then $\displaystyle \frac{m}{n}$ is equal to :