Given an integer, how do you find its opposite?

Which point on the scatter plot is an outlier? a scatter plot is show. point m is located at 3 and 3, point p is located at 5 and 5, point n is located at 5 and 7, point l is located at 6 and 2. additional points are located at 1 and 3, 2 and 3, 2 and 4, 3 and 4, 3 and 5, 4 and 5, 4 and 6, 5 and 6. point p point n point m point l