An industry consists of three firms with sales of $ $225,000,$ $ $485,000,$ and $ $320,000.$ a$.$ Calculate the Herfindahl$-$Hirschman index $($HHI$).$ Instruction: Enter your response rounded to the nearest integer. b$.$ Calculate the four$-$firm concentration ratio $($C$\_4).$ c$.$ Based on the FTC and DOJ Horizontal Merger Guidelines described in the text, is the Department of Justice likely to attempt to block a horizontal merger between two firms with sales of $ $225,000$ and $ $320,000?$ No Yes