The yield of a chemical process is being studied. The two most important variables are thought to be pressure and temperature. Three levels of each factor are selected, and a factorial experiment with two replicates is performed. The yield data are as follows:

Pressure (psig)

Temperature (∘C) 200 215 230 150 90.4 90.7 90.2 90.2 90.6 90.4 160 90.1 90.5 89.9 90.3 90.6 90.1 170 90.5 90.8 90.4 90.7 90.9 90.1

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

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

(c) Under what conditionswould you operate this process?