Решение:
\[ \frac{12-76}{81} = \frac{-64}{81} \]
\[ \frac{-64}{81} : \frac{64}{9} = \frac{-64}{81} \cdot \frac{9}{64} \]
\[ \frac{-1}{9} \cdot \frac{1}{1} = \frac{-1}{9} \]
\[ \frac{-1}{9} \cdot \frac{9}{37} = \frac{-1}{1} \cdot \frac{1}{37} = \frac{-1}{37} \]
Ответ: $$-\frac{1}{37}$$