The rate of change is represented by the slope of each club.
For Club A is 12.
For Club B we calculate using the formula
[tex]m=\frac{y2-y1}{x2-x1}[/tex][tex]\begin{gathered} m=\frac{42-21}{2-1} \\ m=\frac{21}{1}=21 \end{gathered}[/tex]The value is 21.
For Club C we apply the same formula and use the poins shown in the graphic
[tex]\begin{gathered} m=\frac{70-40}{3-1} \\ m=\frac{30}{2} \\ m=15 \end{gathered}[/tex]For club D the slope is the value that is paid each month
which in this case is $20
According to this the greatest rate of chande is for Health Club B
