$$ \frac{9}{14} : 2 - \frac{5}{35} = \frac{9}{14} \cdot \frac{1}{2} - \frac{1}{7} = \frac{9}{28} - \frac{1}{7} = \frac{9}{28} - \frac{1 \cdot 4}{7 \cdot 4} = \frac{9}{28} - \frac{4}{28} = \frac{9-4}{28} = \frac{5}{28} $$
Ответ: $$\frac{5}{28}$$