19. On a number line, point M is the midpoint of .  The coordinate of A and M are  and  respectively.  What is the coordinate of point B?

 

 

Draw a diagram: 

The distance from A to M is 7 – (- 2) = 9 so the distance from M to B must also be 9.

7 + 9 = 16.  The coordinate of B is 16.