a) $$\frac{8}{14} = \frac{4}{7}$$
б) $$\frac{7}{63} = \frac{1}{9}$$
в) $$\frac{30}{84} = \frac{5}{14}$$
г) $$\frac{34 \cdot 12}{3 \cdot 17} = \frac{2 \cdot 12}{3} = \frac{2 \cdot 4}{1} = 8$$