More music: Refer to Exercise 13. Although physical formats sell fewer units than digital formats, their retail

Question:

More music: Refer to Exercise 13. Although physical formats sell fewer units than digital formats, their retail value is higher €” CDs typically sell for $ 15 or more, while a download single typically costs a dollar or less. The following table presents the total number of music units, in millions, sold in each year from 2007 through 2011, and the total retail value, in millions of dollars, of the sold units.

a. Construct a time- series plot for units sold.
b. Construct a time- series plot for total retail value.
c. Explain why the total retail value has been decreasing while the total units sold has been increasing.