What's (8,-2) (r,-6), m = - 4

m is simply the slope of the line. The equation for m or slope is given as:

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

Therefore we can find for r by substituting the values:

- 4 = (-6 - (-2)) / (r - 8)

- 4 = - 4 / (r - 8)

r - 8 = 1

r = 9

So:

(r, - 6) = (9, - 6)