\[\left( - 1\frac{7}{9} \right)^{10} \cdot \left( - 1\frac{7}{9} \right)^{12}\ :\left( - 1\frac{7}{9} \right)^{20} =\]
\[= \left( - 1\frac{7}{9} \right)^{2} = \left( \frac{16}{9} \right)^{2} =\]
\[= \frac{256}{81} = 3\frac{13}{81}\]