$\begin{aligned} & \left(\frac{x^{\frac{1}{3}}}{3}+\frac{x^{\frac{-2}{3}}}{)^{18}}\right. \\ & \mathrm{t}_7={ }^{18} \mathrm{c}_6\left(\frac{\mathrm{x}^{\frac{1}{3}}}{3}\right)^{12}\left(\frac{\mathrm{x}^{\frac{-2}{3}}}{2}\right)^6={ }^{18} \mathrm{c}_6 \frac{1}{(3)^{12}} \cdot \frac{1}{2^6} \\ & \mathrm{t}_{13}={ }^{18} \mathrm{c}_{12}\left(\frac{\mathrm{x}^{\frac{1}{3}}}{3}\right)^6\left(\frac{\mathrm{x}^{\frac{-2}{3}}}{2}\right)^{12}={ }^{18} \mathrm{c}_{12} \frac{1}{(3)^6} \cdot \frac{1}{2^{12}} \cdot \mathrm{x}^{-6} \\ & \mathrm{~m}={ }^{18} \mathrm{c}_6 \cdot 3^{-12} \cdot 2^{-6}: \mathrm{n}={ }^{18} \mathrm{c}_{12} \cdot 2^{-12} \cdot 3^{-6} \\ & \left(\frac{\mathrm{n}}{\mathrm{m}}\right)^{\frac{1}{3}}=\left(\frac{2^{-12} \cdot 3^{-6}}{3^{-12} \cdot 2^{-6}}\right)^{\frac{1}{3}}=\left(\frac{3}{2}\right)^2=\frac{9}{4}\end{aligned}$