You need three formulas

1. Slope formula
m =  with (x1, y1) = (-8,2) and (x2, y2) = (-5,-13)

m = 

m = 

m = 

m = -5 

2. Point-slope formula:
y - y1 = m(x - x1)
y - 2 = -5(x - (-8) )
y - 2 = -5(x + 8)

3. Slope-intercept form:
y = mx + b

We have to get this equation

y - 2 = -5(x + 8)  in that form, which means to solve it for y.
y - 2 = -5x - 40
    y = -5x - 38

Edwin