Nice description. But you've omitted or overlooked the instructions. I'm assuming that you want to find the equation of this linear function.
13-(-2) 15 -5
The slope of this line is m = ----------- = --------- = ----
-4 -2 -6 2
Use the point-slope form of the equation of a straight line:
y-(-2) = (-5/2)(x-2), or y = -2 - (5/2)x + 5, or y = (-5/2)x + 3.