Suppose that a full 24 factorial uses the following factor levels:

Factor Low (−) High(+)

A: Acid strength (%) 85 95 B: Reaction time (min) 15 35 C: Amount of acid (mL) 35 45 D: Reaction temperature (∘C) 60 80 The fitted model from this experiment is ̂y = 24 + 16x1 −

34x2 + 12x3 + 6x4 − 10x1x2 + 16x1x3. Predict the response at the following points:

(a) A = 89, B = 20, C = 38, D = 66

(b) A = 90, B = 16, C = 40, D = 70

(c) A = 87, B = 28, C = 42, D = 61

(d) A = 90, B = 27, C = 37, D = 69