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 measurements [20, 12, 21, 17]; Machine # 2 measurements [ 17, 23, 20, 18]; Machine #3 measurements [ 12, 12, 22, 23]. Using the factors for three sigma control limits, what are x-bar chart upper and lower control limits? Oa. 24.41and 11.76 O b. 26.92and 9.243 O c. 44.08and -7.917 Od. 20.42and 15.74