To find the length of a segment in the number line, you have to subtract the smaller coordinate to the greater coordinate. In the case of the segment XY, its length is:
XY = -6 - (-8) = -6 + 8 = 2
In the case of the segment ZW, its length is:
ZW = 6 - 2 = 4
Given that their lengths are different, then they are not congruent.
