Решим данные уравнения:
a) $$\frac{3}{4} - \left(\frac{7}{8} - a\right) = \frac{1}{8}$$
$$\frac{3}{4} - \frac{7}{8} + a = \frac{1}{8}$$
$$a = \frac{1}{8} - \frac{3}{4} + \frac{7}{8}$$
$$a = \frac{1}{8} - \frac{6}{8} + \frac{7}{8}$$
$$a = \frac{2}{8} = \frac{1}{4}$$
в) $$\frac{3}{4} - \left(x + \frac{1}{12}\right) = \frac{1}{5}$$
$$\frac{3}{4} - x - \frac{1}{12} = \frac{1}{5}$$
$$-x = \frac{1}{5} - \frac{3}{4} + \frac{1}{12}$$
$$-x = \frac{1 \cdot 12}{5 \cdot 12} - \frac{3 \cdot 15}{4 \cdot 15} + \frac{1 \cdot 5}{12 \cdot 5}$$
$$-x = \frac{12}{60} - \frac{45}{60} + \frac{5}{60}$$
$$-x = -\frac{28}{60}$$
$$x = \frac{7}{15}$$
Ответ: а) $$\frac{1}{4}$$, в) $$\frac{7}{15}$$