An industry consists of six firms with sales of $2.1 billion, $5 billion, $0.7 billion, $8 billion, $9 billion and $4 billion. a. Calculate the Herfindahl-Hirschman index (HHI). b. Calculate the four-firm concentration ratio (C4). c. Based on the U.S. Department of Justice's Merger Guidelines described in the text, do you think the Department of Justice would block a horizontal merger between the two firms with sales of $2.1 billion and $5 billion? Explain, and support your explanation with calculations