Решение:
a) $$x+5+(4x-6) = x + 5 + 4x - 6 = 5x - 1$$
б) $$(3x - 2) - (5x - 8) = 3x - 2 - 5x + 8 = -2x + 6$$
в) $$20 + 5(0,2y - 4) = 20 + y - 20 = y$$