\[\left( \frac{3x^{2}y^{- 3}}{z} \right)^{2}\ :\frac{(3x)^{3}z^{- 2}}{y^{5}} =\]
\[= \frac{3^{2}x^{4}y^{- 1}}{3^{3}x^{3}} = \frac{x}{3y}\]