6.4a-6b
7.9a-3b
8. (-6m + n) + (-4m - 5n)
9. (9x² + 5) + (-2x² - 8) + (x² − 3)
10.4a + (9a+3)
11.7b+ (4b-6)
12.8d²+ (6d²-4d)
13. (5x² + 4) + (-3x² - 4)
14. [-4x+ (10-5x)] + 5x
15.8+ [5+ (6 + x)]