You see from the graph that when x = 0, y = 2 so the y-intercept is ( 0 , 2).
you are given points (-6 , 3) and (6 , 1). Find slope:
slope = change in y / change in x
slope = (3 - 1) / (-6 - 6)
slope = 2/-12
slope = -1/6
slope-intercept form: y = mx + b where m = slope and b = y intercept.
y = -1/6x + 2