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Retail e-commerce sales in Germany (excluding event tickets, financial products, and travel) are shown below. German e-Commerce Internet Sales Year (billion euros) 2003 5.8 2004 2005 9.0 2006 10.2 2007 11.4 2008 13.6 (a) Why is a cubic model appropriate for the data? The scatter plot is decreasing and appears to be concave down before changing to concave up. The scatter plot is increasing and appears to be concave down before changing to concave up. The scatter plot is decreasing and appears to be concave up before changing to concave down. The scatter plot is increasing and appears to be concave up before changing to concave down. (b) Align the input to years since 2000. Write the function of the cubic model that gives the retail e-commerce sales in Germany in billion euros, where x is the number of years since 2000, with data from 3 S x S 8. (Round all numerical values to three decimal places.) s ( X) = (c) Write the input value for the approximate location of the inflection point. X =