Combine like terms to simplify expressions

Gather the like terms: same letter, or plain numbers. Add or subtract their numbers, keeping each sign.

1. Simplify (letter term first, then the number): 9y + 3 + 4y + 6
2. Simplify (letter term first, then the number): 7 + 9a + 7a + 5
3. Simplify (letter term first, then the number): n + n + 9 + 4
4. Simplify (letter term first, then the number): 6 + 6w + 1 + 8w
5. Simplify (letters in alphabetical order, number last): y + 9t + 8 + 3y + t
6. Simplify (letters in alphabetical order, number last): 3n + 2x + 8 + 8 + 6
7. Simplify (letters in alphabetical order, number last): 6w + 3 + 5x + 2 + 2x
8. Simplify (letters in alphabetical order, number last): 9m + 6 + 7 + 7a + 9m
9. Simplify (letter term first, then the number): 9a − 3a + 6a + 1 + 3a
10. Simplify (letter term first, then the number): 2m − 2 + 6 + 8m + 7
11. Simplify (letter term first, then the number): 7t + 9 + 1 + 1 − 6
12. Simplify (letter term first, then the number): 9b + 6b + 6 + 2 + 6
13. Simplify (letters in alphabetical order, number last): 5p + 6b + 6 + 8 − 5 + 4p
14. Simplify (letters in alphabetical order, number last): 6 + b + 9y − 4y + b + 8y
15. Simplify (letters in alphabetical order, number last): 1 + 7t + 3y + 9 + 6t + 1
16. Simplify (letters in alphabetical order, number last): 3b + 7 + 9b + 7b + 6x + 9b
17. Simplify (letters in alphabetical order, number last): 17 + 18x − w + 8x − 12 + 6x + 7w + 15w
18. Simplify (letters in alphabetical order, number last): 6 − 15b − 7 + 9 + 16y + 13 + 15 + 19b
19. Simplify (letters in alphabetical order, number last): n + 17x − 5x − 4x + 6 + 5x + 17 + 3
20. Simplify (letters in alphabetical order, number last): y + 3m + 5m + 20m + 7y + 20 + 7y + 19