Use the 2 dots on the line located at (0,1) and (-3,0).
The slope is the change in Y over the change in X:
Change in Y = 0-1 = -1
Change in X = -3 - 0 = -3
Slope = -1 / -3 = 1/3
They intercept in this case is Y1 which = 1.
The equation is y = 1/3x + 1