\[\left( 7\frac{5}{7}\ :3\frac{3}{5} - \frac{1}{7} \right)\ :1\frac{1}{3} =\]
\[= \left( \frac{54 \cdot 5}{7 \cdot 18} - \frac{1}{7} \right)\ :\frac{4}{3} =\]
\[= \left( \frac{15}{7} - \frac{1}{7} \right) \cdot \frac{3}{4} = \frac{14 \cdot 3}{7 \cdot 4} = \frac{3}{2} =\]
\[= 1\frac{1}{2}\]