Answer:
Remember the slope formula:
m= y2-y1/x2-x1
11. (-1,3) (3,3)
= 3-3/3--1
= 0/4
m = 0
12. (1,3) (1, -2)
= -2-3/1-1
= -5/0
= undefined
For the future, know that the slope of horizontal lines is always zero and the slope of vertical lines is always undefined.