\[4\frac{1}{5}\ :\left( \frac{7}{15}\ :\frac{1}{3} \right) = \frac{21}{5}\ :\left( \frac{7 \cdot 3}{15 \cdot 1} \right) =\]
\[= \frac{21 \cdot 5}{5 \cdot 7} = 3\]