\(\left(\frac{2}{3}\right)^x=\left(\frac{9}{4}\right)^{-5}\Rightarrow\left(\frac{2}{3}\right)^x=\left(\frac{3^2}{2^2}\right)^{-5}\Leftrightarrow\left(\frac{2}{3}\right)^x=\left(\frac{3}{2}\right)^{-5.2=-10}\)
\(\Leftrightarrow\frac{2^x}{3^x}=\frac{3^{-10}}{2^{-10}}\Rightarrow2^x.2^{-10}=3^x.3^{-10}\Rightarrow2^{x-10}=3^{x-10}\Leftrightarrow x=10\)