Решение заданий:

1)

1. a) $$2a + (3a - 8b) = 2a + 3a - 8b = (2+3)a - 8b = 5a - 8b$$
2. б) $$-5b - (8a - 5b) = -5b - 8a + 5b = -8a + (-5b + 5b) = -8a + 0 = -8a$$

2)

1. a) $$(5 - 2b) - (7 + 10b) = 5 - 2b - 7 - 10b = (5 - 7) + (-2b - 10b) = -2 - 12b$$
2. б) $$-(3c + 5x) - (9c - 6x) = -3c - 5x - 9c + 6x = (-3c - 9c) + (-5x + 6x) = -12c + x$$

3)

1. a) $$x - (x - 15) + (13 + x) = x - x + 15 + 13 + x = (x - x + x) + (15 + 13) = x + 28$$
2. б) $$(3a - 21) - 2a - (17 - 8a) = 3a - 21 - 2a - 17 + 8a = (3a - 2a + 8a) + (-21 - 17) = 9a - 38$$
3. в) $$6x + (7 - 3x) = 6x + 7 - 3x = (6x - 3x) + 7 = 3x + 7$$
4. г) $$-(4x - 18) + 18 = -4x + 18 + 18 = -4x + 36$$
5. в) $$(2a - 7y) - (5a - 7y) = 2a - 7y - 5a + 7y = (2a - 5a) + (-7y + 7y) = -3a + 0 = -3a$$
6. г) $$(11p + 9c) - (12 + 11p + 9c) = 11p + 9c - 12 - 11p - 9c = (11p - 11p) + (9c - 9c) - 12 = 0 + 0 - 12 = -12$$
7. в) $$(2 - 4b) - (31b - 6) - 11 = 2 - 4b - 31b + 6 - 11 = (2 + 6 - 11) + (-4b - 31b) = -3 - 35b$$
8. г) $$14b - (15b + y) - (y + 10b) = 14b - 15b - y - y - 10b = (14b - 15b - 10b) + (-y - y) = -11b - 2y$$