The easiest way is to compare two different whole-number points. So, the first one is (0,2) and the other is (3,3), meaning that it's 3 right, 1 up. This means that the slope is ⅓. (⅓x)
Next is the point that intercepts the y-axis. In this case, at x=0 y=2. (+2)
So, the equation for the red part is ⅓x+2
