The answer provided does not appear to be correct on your site (6 sigma in minutes= 0.065). Please review and validate.

CheersInc, a small health insurance company, manages its own call center to provide customer service. A call is first taken by a general representative who will try to resolve the client's inquiry. If the general representative cannot assist the client, he will forward the call to the respective specialized unit. As part of its quality control system, management decided that call durations at the general representative level should be between 5 and 7 minutes.

The tables below show the results of 5 samples taken at different hours and the corresponding control limits using the sample data:

In the scenario about CheersInc above, if the call center wants its process at the general representative level to be six-sigma capable, how much should the process standard deviation be in minutes?