The table gives the cumulative sales of iPods since their introduction. s ( x ) = million ipods (b) Write the derivative for the sales model. (Round all numerical values to three decimal places.) s ? ( x ) = million iPods per year (c) Calculate the rate of change of cumulative sales in 2004 . (Round your answer to three decimal places.) milion iPods per year Interpret the rate of change of cumulative sales in 2004. (Round your answer to three decimal places.) In 2004, cumulative iPod sales were by million per year