The table below gives the annual sales (in millions) of a product. year sales 1998 1999 197 2000 2001 2002 2003 2004 2005 2006 215 229 239 245 247 245 239 229 What was the average rate of change of annual sales a) Between 1998 and 1999 b) Between 1998 and 2001 millions of dollars/year millions of dollars/year