-3.6904 and 5.6904 (approx).
Well, 18 and 3 (both factors of 36) add up to 21. As well, the factors 12 and 9 add up to 21.
The factors of -504 are 2, 2, 2, 3, 3, 7 and -1. Then the factors that add to -3 are -24 and 21.
119
They are: 21+6+2 = 29
3551
Although negative numbers aren't usually considered factors, you can use -21, -3 and -2.
The factors of 8 are 1, 2, 4, and 8. The factors that add up to 10 are 2 and 8.
31
factors of 30 that add to 17 are 2 and 15
-1005
167
-261