Решение:

1. a) $$2x - 3y - 11x + 8y = (2x - 11x) + (-3y + 8y) = -9x + 5y$$
2. б) $$5(2a + 1) - 3 = 10a + 5 - 3 = 10a + 2$$
3. в) $$14x - (x - 1) + (2x + 6) = 14x - x + 1 + 2x + 6 = (14x - x + 2x) + (1 + 6) = 15x + 7$$