quality control please solve in steps

Q.3 (6 Points) Control charts are to be established on a certain part dimension. XB and S are given below for 30 samples with subgroup size 4. No. 1 XB 13.18 S 0.22 No. 11 XB 12.98 S 0.10 No. 21 XB 13.04 S 0.23 2 13.11 0.24 12 13.15 0.09 22 13.10 0.20 3 12.78 0.09 13 13.16 0.18 23 13.38 0.20 4 13.26 0.08 14 12.81 0.09 24 12.91 0.10 5 13.10 0.25 15 13.15 0.08 25 13.66 0.15 6 13.73 0.22 16 12.75 0.07 26 13.33 0.62 7 13.21 0.27 17 12.78 0.09 27 12.80 0.23 8 13.18 0.09 18 13.24 0.24 28 12.80 0.17 9 13.33 0.27 19 13.18 0.50 29 12.95 0.09 10 12.94 0.27 20 12.80 0.15 30 13.01 0.10 a. Determine the trial central line and control limits. b. Assume assignable causes are determined, determine the revised central line and control limits