\[\left( 12\frac{2}{5} - 6\frac{1}{5} \right)\ :7\frac{3}{4} =\]
\[= 6\ \frac{2 - 1}{5}\ :\frac{31}{4} = 6\frac{1}{5} \cdot \frac{4}{31} =\]
\[= \frac{31 \cdot 4}{5 \cdot 31} = \frac{4}{5} = 0,8\]