The sum of two remote interior angles (a remote interior angle is the interior angle that is not supplementary to the exterior angle given -- in this case A and B are remote angles) equals the exterior angle.
Y=1 we can check this by looking at the slope of the line: m= so m=0. By looking at the graph we know our y-int is 1. By plugging in this information into the equation of a line we get the following: y=0x+1. That is y=1
