A commuter airline wants to determine the combination of advertising medium (four levels) and advertising agency (two levels) that would produce the largest increase in ticket sales per advertising dollar spent. Each of the two advertising agencies has prepared advertisements in formats required for distribution by each of the media (including television, radio, newspaper, and Web site). Forty small towns of roughly the same size have been selected for this experiment. Furthermore, groups of five of these small towns have been assigned to receive an advertisement prepared and distributed by each of the eight agency–medium combinations. The dollar increases in ticket sales per advertising dollar spent, based on a one-month period, are listed in the file P19_36.xlsx. Test for any significant main effects and interactions at the 5% level, and briefly summarize your results.