\[x = 4\frac{1}{3}:\]
\[- 7,9 - x = - 7\frac{9}{10} - 4\frac{1}{3} =\]
\[= - \left( 7\frac{27}{30} + 4\frac{10}{30} \right) = - 11\frac{37}{30} =\]
\[= - 12\frac{7}{30}.\]