There are no numbers that are able to do this.
The factors of -20 are:
1 and 20
2 and 10
4 and 5
one of either number can be negative in this instance.
The only ways to add up to 6 are:
0 and 6
1 and 5
2 and 4
3 and 3
Addition with negatives to 6:
10 and -4
9 and -3
8 and -2
7 and -1
or -6 multiplied by -1
I don't see any ways to get to 6 using addition and -20 by multiplication
