Ответ:

1) 5x - (3x + 5) + (2x - 4) = 5x - 3x - 5 + 2x - 4 = 4x - 9

2) 1/8c - (5/6c - 1/4c) = 1/8c - 5/6c + 1/4c = (1/8 - 5/6 + 1/4)c = (-11/24)c

3) 1/3(0.3a - 0.6) - 1/4(0.4a - 0.8) = (0.1a - 0.2) - (0.1a - 0.2) = -0.4