Oil producers are interested in high strength nickel alloys that are strong and corrosion resistant. An experiment conducted in which yield strengths were compared for nickel alloy tensile specimens charged in sulfuric acid solution saturated with carbon disulfide. Two alloys were combined; a 75% nickel composition and a 30% nickel composition. The alloys were tested under two different charging times, 25 and 50 days. A 23 factorial was conducted with the following factors % sulfuric acid 4%, 6%: (xi) charging time 25 days, 50 days: (#2) nickel composition 30%, 75%: (2:3). A specimen was prepared for each of the eight conditions. Since the engineers were not certain of the nature of the model (i.e., whether or not quadratic terms would be needed), a third level (middle level) was incorporated and four center runs were employed using four specimens at 5% sulfuric acid, 37.5 days, and 52.5% nickel composition. The following are the yield strengths in kilograms per square inch. The center runs give the following strengths: 51.6, 51.4, 52.4, 52.9(a) Test to determine which main effects and interactions should be involved in the fitted model.(b) Test for quadratic curvature.(c) If quadratic curvature is significant, how many additional elesign points are needed to determine which quadratic terms should be included in themodel

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Charging Time 50 Days Sulfuric Acid 25 Days Nickel Sulfuric Acid Comp. 75% 30% 6% 4% 4% 47.9 6% 47.2 41.7 50.2 50.8 47.4