a) 7 12 - 5 36; б) 10 13 - 4 52; в) 13 42 - 3 14; г) 31 48 - 7 12.

а)
\( \frac{7}{12} - \frac{5}{36} = \frac{21}{36} - \frac{5}{36} = \frac{16}{36} = \frac{4}{9} \)

б)
\( \frac{10}{13} - \frac{4}{52} = \frac{40}{52} - \frac{4}{52} = \frac{36}{52} = \frac{9}{13} \)

в)
\( \frac{13}{42} - \frac{3}{14} = \frac{13}{42} - \frac{9}{42} = \frac{4}{42} = \frac{2}{21} \)

г)
\( \frac{31}{48} - \frac{7}{12} = \frac{31}{48} - \frac{28}{48} = \frac{3}{48} = \frac{1}{16} \)