D Question 4 A quality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are under control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results: Machine # 1 #2 # 3 Measurements 17 15 15 17 16 25 18 25 23 24 23 22 What are the x-bar chart three-sigma upper and lower control limits