Determine the rate of change_Curb

In 2008, about 66 million U.S. households had both landline phones and cell phones. This number decreased by an average of 5 million households per year. Use the table below to calculate the rate of change for the interval [2008, 2011].
  1. Determine the interval to be observed.
  2. Determine .
  3. Determine .
  4. Substitute ) and into the slope formula to calculate the rate of change.