Positive integer pairs that you can add together to make 18 are:
1 + 17
2 + 16
3 + 15
4 + 14
5 + 13
6 + 12
7 + 11
8 + 10
9 + 9
And those sums' reverses.
food
-18 and -18
The numbers are: -6 and 3
-1
They are: 18+14 = 32 and 18-14 = 4
54
2+5+11= 18.
15
9 9
18
20
21
-1