4. Найти значение выражения a) - 1/8 + 3/4 б) - 16/21 - 4/7 B) 3/5 * (-1/9) г) 5/8 * 1/4

a) $$-\frac{1}{8} + \frac{3}{4} = -\frac{1}{8} + \frac{6}{8} = \frac{5}{8}$$

б) $$\frac{-16}{21} - \frac{4}{7} = \frac{-16}{21} - \frac{12}{21} = \frac{-28}{21} = -\frac{4}{3} = -1\frac{1}{3}$$

в) $$\frac{3}{5} \cdot \left(-\frac{1}{9}\right) = -\frac{3}{45} = -\frac{1}{15}$$

г) $$\frac{5}{8} \cdot \frac{1}{4} = \frac{5}{32}$$