Well I have an Idea but I'm not sure if this is correct:

we have 5 +3 8 -7 1 -1 0 +1 1 +7 8 -2 6 -4 2 +2 4

If we now grab the italic numbers we have: +3-7-1+1+7-2-4+2 = -1

If we take the row: 5, 8, 1, 0, 1, 8, 6, 2, 4, and add this -1 we get the number 3

Well I have an Idea but I'm not sure if this is correct:

we have 5 +3 8 -7 1 -1 0 +1 1 +7 8 -2 6 -4 2 +2 4

If we now grab the italic numbers we have:

+3-7-1+1+7-2-4+2 = -1

If we take the row:

5, 8, 1, 0, 1, 8, 6, 2, 4, and add this -1 we get the number 3