1.The yield of a chemical process is being studied. The two most important variables are thought to be the pressure and the 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