A line contains the points (a-4, b+4) and (a, b). What is the slope of the line.

The slope m of the line that joins  any two points (x1,y1) and
(x2,y2) is given by:

m =
(y2-y1)/(x2-x1)....(1)

The given two points are (a-4 , b+4)  and
(a,b).

Here x1 = a-4 , y1 = b+4 and x2 = a and y2 =
b.

Therefore ,we substitute the coordintes of the given points in
the formula at (1) to obtain the slope.

m = {b-(b+4)}/{a-
(a-4)}.

m = (-4)/(4).

m =
-1.

Therefore the slope of the line joining the points (a-4, b+4)
and (a , b) is -1.