2 7 -- + -- = 9 18

$$\frac{2}{9} + \frac{7}{18} = \frac{2 \cdot 2}{9 \cdot 2} + \frac{7}{18} = \frac{4}{18} + \frac{7}{18} = \frac{11}{18}$$

Ответ: $$\frac{11}{18}$$