Part a
we have the points (3,7) and (3,-4)
Note that the x-coordinates are equal
that means
Is a vertical line (parallel to the y-axis)
that means
the slope is undefined
Verify
m=(-4-7)/(3-3)
m=-11/0 ----> undefined
Part b
we have the points (-2,5) and (9,5)
Note that the y-coordinates are equal
That means
Is a horizontal line (parallel to the x-axis)
The slope is zero
Verify
m=(5-5)/(9+2)
m=0/11
m=0