\[2\frac{1}{4}\ :\left( \frac{3}{8}\ :\frac{1}{5} \right) = \frac{9}{4}\ :\left( \frac{3}{8} \cdot \frac{2}{1} \right) =\]
\[= \frac{9 \cdot 4}{4 \cdot 3} = 3\]