1. 6x - 2x + 3y - Commutative
(6x - 2x) + 3y - Associative
3x + 3y
2. 5a - 2a + 3z - z - Commutative
(5a - 2a) + (3z - z) - Associative
3a + 2z
3. 10b - 2b + 4b + 7c - 9 - Commutative
(10b - 2b) + 4b + 7c - 9 - Associative
(8b + 4b) + 7c - 9 - Associative
12b + 7c - 9
4. 9m - 8m + 6n - 7n - Commutative
(9m - 8m) + (6n - 7n) - Associative
1m - 1n or m - n