First determine the slope of the line by picking 2 coordinates on the graph. X1=8,y1=240. X2=10,y2=300. Now plug in the slope formula. (300-240)/(10-8) . The slope is the rise(y2-y1)/(x2-x1)

m=60/2=30

Now to get the y intercept use the equation y=mx+b. The y intercept is where y=0