First I chose two points on the line that fall on 2 intervals or 2 lines. Then if found the slope of the two points. Using the slope and one of the points I pugged the numbers into an equation to solve for b. Once I found b I wrote an equation using b and the slope.
y=-2/3+300
steps:
(250,200)(300,100)
100-200/300-150
-100/150 or -2/3
100=-2/3(300)+b
100=-200+b
300=b
y=-2/3b+300