a) $$ \frac{5}{7} - \frac{2}{7} = \frac{5-2}{7} = \frac{3}{7} $$
б) $$ \frac{8}{12} - \frac{3}{12} = \frac{8-3}{12} = \frac{5}{12} $$
в) $$ \frac{9}{36} - \frac{7}{36} = \frac{9-7}{36} = \frac{2}{36} $$
г) $$ \frac{258}{100} - \frac{16}{100} = \frac{258-16}{100} = \frac{242}{100} = 2 \frac{42}{100} = 2 \frac{21}{50} $$
Ответ: $$ \frac{3}{7}; \frac{5}{12}; \frac{2}{36}; 2 \frac{21}{50} $$