Explanation:
the slope of a line is the ratio
y coordinate difference / x coordinate difference
when going from one point on the line to another.
so, when going from (2, 6) to (9, 3) :
x changes by +7 (from 2 to 9).
y changes by -3 (from 6 to 3).
therefore, the slope is -3/+7 = -3/7