Найдите значение выражения: a) $(\frac{5}{6} + \frac{4}{9}) - \frac{5}{4}$ б) $2 \frac{2}{8} + (3 \frac{1}{3} - 2 \frac{3}{5}) : \frac{7}{15}$

a) $(\frac{5}{6} + \frac{4}{9}) - \frac{5}{4} = (\frac{15}{18} + \frac{8}{18}) - \frac{5}{4} = \frac{23}{18} - \frac{5}{4} = \frac{46}{36} - \frac{45}{36} = \frac{1}{36}$; б) $2 \frac{2}{8} + (3 \frac{1}{3} - 2 \frac{3}{5}) : \frac{7}{15} = 2 \frac{1}{4} + (\frac{10}{3} - \frac{13}{5}) : \frac{7}{15} = \frac{9}{4} + (\frac{50}{15} - \frac{39}{15}) : \frac{7}{15} = \frac{9}{4} + \frac{11}{15} : \frac{7}{15} = \frac{9}{4} + \frac{11}{15} \cdot \frac{15}{7} = \frac{9}{4} + \frac{11}{7} = \frac{63}{28} + \frac{44}{28} = \frac{107}{28} = 3\frac{23}{28}$