To find the slope of (-7,-18) and (-12,-3) we need to subtract the two from each other.
(-7,-18)
-(-12,-3)
(5,-15)
Now we turn that fraction into the slope. Rise (y) over Run (x) -15/5 = -3
y = mx + b
M is our slope.
y = -3(x) + b
Now we can solve for b, by plugging in one of the points.
-3 = -3(-12) + b
-3 = 36 + b
-39 = b. Now your equation is y = -3(x) -39. Hope this helped!
-TTL