The factors that influence the breaking strength of a synthetic fiber are being studied. Four production machines and three operators are chosen and a factorial experiment is run using fiber from the same production batch. The results are as follows:

Machine Operator 1 2 3 4 1 109 110 108 110 110 115 109 108 2 110 110 111 114 112 111 109 112 3 116 112 114 120 114 115 119 117

(a) Analyze the data and draw conclusions. Use ???? = 0.05.

(b) Prepare appropriate residual plots and comment on the model’s adequacy.