The rate is given by the slope which is defined by:
[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]
The first line passes throught the points (0,0) and (21,1); hence its rate is:
[tex]\begin{gathered} m=\frac{21-0}{1-0} \\ m=\frac{21}{1} \\ m=21 \end{gathered}[/tex]
Therefore, the rate of change of the first line is 21 mph.
Using the points given for the second line we have:
[tex]\begin{gathered} m=\frac{68-51}{4-3} \\ m=\frac{17}{1} \\ m=17 \end{gathered}[/tex]
Therefore, the rate of change of the second line is 17 mph.
