Given two points, (x1, y1) and (x2, y2), the slope can be found by ...
... slope = (change in y)/(change in x) = (y2-y1)/(x2-x1)
For your given points, the slope is
... slope = (79 -(-20))/(9 -(-2)) = 99/11 = 9
The point-slope equation for a line with slope m through point (h, k) is
... y -k = m(x -h)
You have m=9, h=-2, k=-20, so the equation is
... y +2 = 9(x +20)