Table shows the number of wireless service subscribers in the United States and their average monthly bill in the years from 2000 through 2015. \begin

Transformations of functions
Table shows the number of wireless service subscribers in the United States and their average monthly bill in the years from 2000 through 2015. \begin{matrix} \text{Year} & \text{Subscribers} & \text{Average Monthly}\ \text{ } & \text{(millions)} & \text{Revenue per Subscriber Unit (\$)}\ \text{2000} & \text{109.5} & \text{48.55}\ \text{2001} & \text{128.4} & \text{49.79}\ \text{2002} & \text{140.8} & \text{51.00}\ \text{2003} & \text{158.7} & \text{51.55}\ \text{2004} & \text{182.1} & \text{52.54}\ \text{2005} & \text{207.9} & \text{50.65}\ \text{2006} & \text{233.0} & \text{49.07}\ \text{2007} & \text{255.4} & \text{49.26}\ \text{2008} & \text{270.3} & \text{48.87}\ \text{2009} & \text{285.6} & \text{47.97}\ \text{2010} & \text{296.3} & \text{47.53}\ \text{2011} & \text{316.0} & \text{46.11}\ \text{2012} & \text{326.5} & \text{48.99}\ \text{2013} & \text{335.7} & \text{48.79}\ \text{2014} & \text{355.4} & \text{46.64}\ \text{2015} & \text{377.9} & \text{44.65}\ \end{matrix} One of the scatter plots suggests a linear model. Use the points at t = 0 and t = 15 to find a model in the form y = mx + b.

Use $$(t_1,y_1)=(0,109.5)$$ and $$(t_2,y_2)=(15,377.9)$$ to find the slope:
$$\displaystyle{m}=\frac{{{y}{2}-{y}{1}}}{{{t}{2}-{t}{1}}}=\frac{{{377.9}-{109.5}}}{{{15}-{0}}}\sim{17.9}$$