Explanation:
since it is in the same line as DE, both have the same slope.
the slope is the ratio of "y coordinate change / x coordinate change" when going from one point on the line to another.
and so by using the coordinates of D and E
x changes by +4 (from 8 to 12).
y changes by -8 (from 32 to 24).
the slope is therefore
-8/+4 = -2