9) +7 = 27 18

$$\frac{8}{27}+\frac{7}{18} = \frac{8 \cdot 2}{27 \cdot 2} + \frac{7 \cdot 3}{18 \cdot 3} = \frac{16}{54}+\frac{21}{54} = \frac{37}{54}$$

Ответ: $$\frac{37}{54}$$