7 9/10 + (-1 6/5)=

$$7 \frac{9}{10} + (-1 \frac{6}{5}) = 7 \frac{9}{10} - 1 \frac{6}{5} = 7 \frac{9}{10} - 1 \frac{12}{10} = 6 \frac{19}{10} - 1 \frac{12}{10} = 5 \frac{7}{10} = 5,7$$

Ответ: 5,7