Please help with this!

The table below gives the annual sales (in millions) of a product. year 1998 1999 2000 2001 2002 2003 2004 2005 2006 sales 152 179 200 215 224 227 224 215 200 What was the average rate of change of annual sales a) Between 2003 and 2004 millions of dollars/year b) Between 2003 and 2005 millions of dollars/year