What is the rule if: xy
x y
3 1

9 3

15 5

y - 1 = (1/3)(x - 3)

Step-by-step explanation:

By inspection we see that if x increases by 6, y increases by 2.  Thus, the slope of the line connecting 2 or more of these points is m = 2/6, or m = 1/3.

Using the point-slope formula y - k = m(x - h), we substitute 1/3 for m, 3 for h and 1 for k, obtaining:

y - 1 = (1/3)(x - 3)