\[2\frac{1}{4}\ a^{- 1}b^{3} \cdot \left( \frac{2}{9}a^{2}b^{- 3} \right) =\]
\[= \frac{9}{4} \cdot \frac{2}{9} \cdot a^{- 1 + 2} \cdot b^{3 - 3} =\]
\[= \frac{1}{2}a^{1}b^{0} = \frac{1}{2}\text{a.}\]