Allow me to answer this question by giving you an example:
The slope of the line is: m= (Ysub2 - Ysub1) / (Xsub2 - Xsub1), where m is the slope of the line and Xsub1 is not equal to Xsub2.
Let the first ordered pair (4, 8) be called (Xsub1, Ysub1) and the second ordered pair (1, 6) be called (Xsub2, Ysub2).
Substituting the values for the slope,we have
m = (6-8) / (1-4)
m = -2 / -3
m = 2/3 Therefore the slope of the line is 2/3.