Directions: Simplify these problems by combining like terms.
1. 9s + 2s - 3s - 6
2. 12t - 4t - 6 + 5t
3. 18r + 13r + 4r - 3r =
4. 21 - 4q + 42r - 16 =
5. 19st - 6s + t =
6. 107 + 107x - x =
7. 15a2 - 12a + a2 - 3a
8. 13t + 14t + t =
9. r + s + rs +2s + rs + s=
10. 5pt - 3p + 4t - 2pt =
11. 13x2 + 3x2 - x =
12. 103c - 5c + 9c =
13. 11q - 4 + 10q - 5q + 9 =
14. 2k - 28k + 3k =
15. 183x + 91x - 23x =