Find the slope of the line that passes through (-66, -21) and (-67, 20)

The straight line is given by the equation
y=kx+b
We substitute coordinates of points 
-21=-66k+b (1)
2=-67k+b (2)
We give a system of equations
Solution of this system:
(1) b=66k-21
(2) 20=-67k+66k-21
20=-k-21
k=-21-20
k=-41
b=-41*66-21=-2727
y=-41x-2727