Question

What is the slope of the line between (3, -4) and (-2, 1)?

Answer 1

What is the slope of the line x = -5?

Answer 2

That's a simple formula:\[\frac{ y-y _{1} }{ x-x _{1} }\]
Pick out one of you points and fill in the x and y.
(3,-4)
-4-y / 3-x
Pick out the next point.
(-2,1)
-4-1/3--2
-5/5,
which equals -1.
And there you go

Answer 3

And for your next question, the slope of a vertical line like that one should be undefined. Horizontal lines will always be 0.