The table below gives the annual sales (in millions) of a product. year 1998 1999 2000 2001 2002 2003 2004 2005 2006 sales 268 313 348 373 388 393 388 373 348 What was the average rate of change of annual sales a) Between 1999 and 2000 millions of dollars/year b) Between 1999 and 2004 millions of dollars/year