(a) If there are only three firms in an industry in a country, then what would the four firm concentration ratio (C4) for this industry be equal to? Please show your calculations. (b) There is only one firm in the United States (Boeing) that manufactures large passenger aircraft (large passenger aircraft is definbed as aricraft that can transport more than 150 passengers). The C4 for this industry would therefore be 1 as C4 is based on only US data. Why might Boeing face some competition in the market for large passenger aircraft even though the C4 would imply that Boeing faces no competition at all? Please give an explanation.