Below is the Stockholders Equity Section of the Balance Sheet for Walgreens Boots Alliance, Inc. for the fiscal year ended 2019 (in millions). Review this excerpt and answer the following questions:

a. The dollar amount in the common stock account is $12 million. How was this computed?

b. Why is there no number shown in the preferred stock account?

c. What is the difference in the dollar amount of treasury stock from 2018 to 2019 expressed as a % and what does this mean?