15.22 Samples of six different brands of diet or imitation margarine were analyzed to determine the level of physiologically active polyunsaturated fatty acids (PAPUFA, in percent), resulting in the data shown in the accompanying table. (The data are fictitious, but the sample means agree with data reported in Consumer Reports.)

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Imperial 14.1 13.6 14.4 14.3 Parkay 12.8 12.5 13.4 13.0 12.3 Blue Bonnet 13.5 13.4 14.1 14.3 Chiffon 13.2 12.7 12.6 13.9 Mazola 16.8 17.2 16.4 17.3 18.0 Fleischmann's 18.1 17.2 18.7 18.4 a. Test for differences among the true average PAPUFA percentages for the different brands. Use a = .05. b. Use the T-K procedure to compute 95% simultane- ous confidence intervals for all differences between means and give the corresponding underscoring pattern.