7 \cdot 2\frac{6}{7} + \frac{53}{12} : (\frac{7}{9} - \frac{9}{4})

Решим пример по действиям:

1) $$7 \cdot 2\frac{6}{7} = 7 \cdot \frac{20}{7} = 20$$

2) $$(\frac{7}{9} - \frac{9}{4}) = (\frac{28}{36} - \frac{81}{36}) = -\frac{53}{36}$$

3) $$\frac{53}{12} : (-\frac{53}{36}) = \frac{53}{12} \cdot (-\frac{36}{53}) = -\frac{36}{12} = -3$$

4) $$20 + (-3) = 20 - 3 = 17$$

Ответ: 17