Option C:
The rate of change is $3 per picture.
Solution:
Rate of change is same as the slope of the line.
Take any two points on the graph.
(0, 20) and (20, 80) are two points on the line of the graph.
[tex]x_1=0, y_1=20, x_2=20, y_2=80[/tex]
Slope of two points formula:
[tex]$m=\frac{y_2-y_1}{x_2-x_1}[/tex]
[tex]$m=\frac{80-20}{20-0}[/tex]
[tex]$m=\frac{60}{20}[/tex]
[tex]$m=\frac{3}{1}[/tex]
m = 3
The rate of change is $3 per picture.
Hence option C is the correct answer.
