$$7 \frac{7}{9} + 2 \frac{2}{9} = (7 + 2) + (\frac{7}{9} + \frac{2}{9})$$
$$= 9 + \frac{7+2}{9} = 9 + \frac{9}{9} = 9 + 1 = 10$$
Ответ: 10