Question 750105
2 points define a line. (1,3) (3,1) is what I'll use. 

slope-intercept is the form y=mx+b where m is the slope and b is the y intercept.

m=(y2-y1)/(x2-x1)= (1-3)/(3-1) = -2/2 = -1 

with the slope, we substitute a point into this equation -

y-3=-1(x-1)

y-3=-1x+1 (distribute the -1 over the two terms)

y=-1x+4  (add 3 to both sides to simplify)

Now - you should double check that the equation works for the extra two pairs we didn't use. To be sure there were no mistakes along the way, and no typo in the question)