Ok so this question:
y + 1 = - ( x - 2 ) (distribute the negative inside the parenthesis)
y + 1 = -x + 2 (substitute the y= -1)
-1 + 1 = -x + 2
0 = -x + 2 (take two to the other side)
-2 = -x (divide the negative away from x)
2 = x
The GCF of those numbers is 2