\[\left( \left( 12\frac{5}{8} - 10,5 \right)\ :\frac{5}{8} - 2\frac{3}{5} \right)\ :\frac{3}{4} =\]
\[= \left( \frac{101}{8} \cdot \frac{8}{5} - \frac{21}{2} \cdot \frac{8}{5} - \frac{13}{5} \right) \cdot \frac{4}{3} =\]
\[= \left( \frac{101}{5} - \frac{84}{5} - \frac{13}{5} \right) \cdot \frac{4}{3} = \frac{4}{5} \cdot \frac{4}{3} =\]
\[= \frac{16}{15} = 1\frac{1}{15}.\]