In 1998 federal vehicle emission standards allowed 3.4 hydrocarbons released per mile driven. By 2006, the standards allowed only 0.2 hydrocarbons per mile driven. What was the annual rate of change from 1998 to 2006?

So the annual rate of change of the hydrocarbon release can be solve by:

Annual rate of change = (old hydrocarbon - new hydrocarbon) / (old year - new year)

Annual rate of change = (3.4 - 0.2) / (1998 - 2006)

Annual rate of change = - 0.0175 hydrocarbon release per mile per year