Question: Simplify the following two expressions:

a) \[{{\left( \frac{3{{x}^{2}}{{y}^{-3}}}{2x{{y}^{2}}} \right)}^{3}}\] b) 7 \[\sqrt{27x{{y}^{2}}}-4\sqrt{75x{{y}^{2}}}+2\sqrt{12x{{y}^{2}}}\]