what equation represents the graphed function

From the graph you can see easily that the y-intercept is (0,3).

The line passes thru the 2 given points (0,3) and (3,2).
                                                           2-3
Thus, the slope of this line is    m  = -------- = -1/3
                                                           3- 0

and so the equation of the graphed line is    y = (-1/3)x + 3.