A critical dimension of the service quality of a call center is the wait time of a caller to get to a sales representative. Periodically, random samples of 6 customer calls are measured for time. Results from the last six samples of n = 7 are given in the following table.

a)    Management is willing to use 3-sigma limits. Using the factors in Table, justify upper and lower limits for mean and range charts.
b)    place sample means and ranges on their respective control charts. Is the process in control?