Solve this questions please: the correct answer for the first part should be 16.08 for UCL and 15.92 for LCL please show me how you got that answer:

- S6.8 Bill Kime's bowling ball factory makes bowling balls of adult size and weight only. The standard deviation in the weight of a bowling ball produced at the factory is known to be 0.12 pounds. Each day for 24 days, the average weight, in pounds, of nine of the bowling balls produced that day has been assessed as follows: a) Establish a control chart for monitoring the average weights of the bowling balls in which the upper and lower control limits are each two standard deviations from the mean. What are the values of the control limits? b) If three standard deviations are used in the chart, how do these values change? Why