Find the slope, if it exists, of the line containing the pair of points

Question

(9,1) and (10,-7)

The slope m = __

or the slop is undefined

Answer 1

m=(y1-y2)/(x1-x2)

does not exist if the denominator = 0

Answer 2

Thank you, I could not remember the formula to use.
this is what I got:

M = 1 + 7/ 9 - 10 = 8/-1

I'm still not sure what the slope is.

Thanks in advance for you help.

Answer 3

(1+7)/(9-10)

= 8/-1

= -8