Answers are:
1. 6s + 2s - 3s - 6 = 5s - 6
2. 10t - 4t -6 + 5t = 11t - 6
3. 18r + 18r + 9r - 3r = 42r
4. 20 - 4q + 40r - 16 = -4q + 40r + 4
5. 17st - 16s + t = - 16s + 17st + t
6. 101+101x - x = 100x + 101
7. 16a2 - 14a + a2 - 3a = 17a2 - 17a
8. 14t + 14t + t = 29t
9. r + s + rs + s + rs + s = r + 2rs + 3s
10. 54 pt - 3p + 4t - 3pt = -3p + 51pt + 4t
11. 14x2 + 3x2 - x = -x + 17x2
12. 101c - 5c +4c = 100c
13. 12q - 4 + 10q - 4q +9 = 18q + 5
14. 21k - 20k + 3k = 4k
15. 181x + 91x - 23x = 249x
Explanation: If a term contains several variables, it is standard to put the variables in alphabetical order.
Your correct answers may not be in this order.