б) $$(6 - 2\frac{4}{5}) \cdot 3\frac{1}{8} - 1\frac{3}{5} : \frac{1}{4}$$

$$(6 - 2\frac{4}{5}) \cdot 3\frac{1}{8} - 1\frac{3}{5} : \frac{1}{4} = (6 - \frac{14}{5}) \cdot \frac{25}{8} - \frac{8}{5} : \frac{1}{4} = (\frac{30}{5} - \frac{14}{5}) \cdot \frac{25}{8} - \frac{8}{5} \cdot 4 = \frac{16}{5} \cdot \frac{25}{8} - \frac{32}{5} = \frac{2}{1} \cdot \frac{5}{1} - \frac{32}{5} = 10 - \frac{32}{5} = \frac{50}{5} - \frac{32}{5} = \frac{18}{5} = 3\frac{3}{5}$$ Ответ: $$3\frac{3}{5}$$