Answer
$\approx 6.54$ million more tax returns were made each year from 2007 to 2014 through e-file
Work Step by Step
Evaluate the expression:
$\dfrac{f(2014)-f(2007)}{2014-2017}=\dfrac{125.8-80}{7}\approx 6.54$
This means that around 6.54 million more tax returns were made each year from 2007 to 2014 through e-file.
