6) 11+7=

$$1\frac{11}{18}+\frac{7}{15} = 1\frac{11 \cdot 5}{18 \cdot 5}+\frac{7 \cdot 6}{15 \cdot 6} = 1\frac{55}{90}+\frac{42}{90} = 1\frac{97}{90} = 1 + 1\frac{7}{90} = 2\frac{7}{90}$$

Ответ: $$2\frac{7}{90}$$