б) (5c+8+9d)-6+ +3-(4c-2-d);

б) $$(5c + 8 + 9d) \cdot 6 + 3 \cdot (4c - 2 - d) = 5c \cdot 6 + 8 \cdot 6 + 9d \cdot 6 + 3 \cdot 4c - 3 \cdot 2 - 3 \cdot d = 30c + 48 + 54d + 12c - 6 - 3d = (30c + 12c) + (54d - 3d) + (48 - 6) = 42c + 51d + 42$$ Ответ: $$42c + 51d + 42$$