In order to find the rate of change of the given line, use the following formula:
[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]where (x1,y1) and (x2,y2) are two points of the line.
From the given graph you can select any pair of points, for example:
(x1,y1) = (2,400)
(x2,y2) = (4,1200)
replace the values of the previous coordinates in the formula for m:
[tex]m=\frac{1200-400_{}}{4-2}=\frac{800}{2}=400[/tex]Hence, the rate of change is 400
