31
34
26
79
-20 and 2
First list the factors of each. For 18, that's 1, 2, 3, 6, 9, and 18. For 20, that's 1, 2, 4, 5, 10, and 20. From these, you could add all of the factors of 18 to get 39. Or you could add 20, 10, and 9. Or 20, 10, 5, and 4. Or . . . you get the idea.
15 and 4 are the factors of 120 that add up to 19.
Factors multiply. The same set of numbers won't add up to both 140 and 240, but 120 and 20 are factors of 240 that total 140.
146
-13
1, 4, and 20. There are other factors, too.
34