[tex]\bf \left[ \left( \cfrac{3mn}{2} \right)^{-1} \right]^{-4}\implies \left[ \left( \cfrac{2}{3mn} \right)^{1} \right]^{-4}\implies \left[ \cfrac{2}{3mn} \right]^{-4}\implies
\left[ \cfrac{3mn}{2} \right]^{4}
\\\\\\
\left[ \cfrac{3^4m^4n^4}{2^4} \right]\implies \cfrac{81m^4n^4}{16}[/tex]
