we have to find the slope of the line that passes through this points:
p1(-2,15), p2(-8,-5)
the slope of a line through two points is calculated like this:
m = (y2 - y1)/(x2 - x1)
where x1,y1,x2,y2 are the coordinates of the two points, so we have:
m = (-5 - 15)/(-8 - (-2))
m = (-20)/(-8 + 2)
m = -20/-6
m = 10/3
that is the line slope