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Perform the indicated operation:
1. (9a + 5b) + (2a + 2b) + (6a – 12b) =
2. (-8c + d) – (-7c + 2d) =
3. (4x +7y – 9) + (8x + 3y + 1) =
4. (5x + 9y – 7) – (7x +2y + 3) =
5. (3x2 + 4x – 2) – (x2 – 5x + 7) = ​