The slope of the line is given by the formula
m=(y2-y1)/(x2-x1)
we have
(x1,y1)=(-5,8)
(x2,y2)=(-5,9)
substitute the values in the formula
m=(9-8)/(-5+5)
m=1/0
is undefined
The slope of the line is undefined because is a vertical line
Part 2) Find the slope of the line containing the following points: (8,-6) (9,-6)
we have
(x1,y1)=(8,-6)
(x2,y2)=(9.-6)
substitute in the formula
m=(-6+6)/(9-8)
m=0/1
m=0
The slope of the line is zero because is a horizontal line