For (-7,3) and (5,3) the answer is 12. You add the different points, -7 and 5 because one is negative and one is positive. You do not add 3 and 3 because they are the same.
(3,-6) and (3,-10) = 4 because -6 and -10 are negatives. The answer is always positive.
(8,0) and (8,-8) = 8.
