2) 6 4/9+5 5/9

$$6 \frac{4}{9}+5 \frac{5}{9} = (6+5) + (\frac{4}{9} + \frac{5}{9}) = 11 + \frac{4+5}{9} = 11 + \frac{9}{9} = 11 + 1 = 12$$.

Ответ: 12