8) 1,2 (4-7)-1.8(3-4) при а-4: r) 2(+6)-7(3-4) при

в) 1,2(a - 7) - 1,8(3 - a) при a = 4 1/3

1,2(a - 7) - 1,8(3 - a) = 1,2a - 8,4 - 5,4 + 1,8a = 3a - 13,8

a = 4 1/3 = 13/3

3a - 13,8 = 3 * 13/3 - 13,8 = 13 - 13,8 = -0,8

Ответ: $$-0,8$$

г) $$2\frac{1}{2}(a + 6) - 7\frac{2}{3}(3 - a) \text{ при } a = 0,7$$

$$2\frac{1}{2}(a + 6) - 7\frac{2}{3}(3 - a) = \frac{5}{2}(a + 6) - \frac{23}{3}(3 - a) = \frac{5}{2}a + 15 - 23 + \frac{23}{3}a = (\frac{5}{2} + \frac{23}{3})a - 8 = (\frac{15}{6} + \frac{46}{6})a - 8 = \frac{61}{6}a - 8$$

a = 0,7 = 7/10

$$\frac{61}{6}a - 8 = \frac{61}{6} \cdot \frac{7}{10} - 8 = \frac{427}{60} - 8 = \frac{427}{60} - \frac{480}{60} = -\frac{53}{60}$$

Ответ: $$- \frac{53}{60}$$