First you find all factors of -30:
1 & -30, 2 & -15, 3 & -10, 5 & -6, 6 & -5, 10 & -3, 15 & -2, 30 & -1
Then you add each pair together:
1 - 30 = -29
2 - 15 = -13
3 - 10 = -7
5 - 6 = -1
6 - 5 = 1
10 - 3 = 7
15 - 2 = 13
30 - 1 = 29
And find that the answer is 6 & -5.