Ab lies on a number line. the coordinate of point a is -6. given that ab= 20, what are the two possible coordinates for point b?

The fact that you must remember is that these points lie on a plane that have a a distance that is ALWAYS an absolute value.  If point A lies on -6 you can have two points that are of a distance 20 points in either direction.  If moving the left, point B can have a value of -26 and moving to the right, point B will have a value of 14.  Hope this is clear!

Good luck!