How do I find standard deviation? I need to calculate CP and CPK.

Question below:

The three most important quality attributes at Mike's Super Service fast-food restaurant are considered to be good food, fast services, and a clean environment. The restaurant manager uses a combination of customer surveys and statistical measurement tools to monitor these quality attributes. A national marketing and research firm has developed data showing that when customers are in line up to five minutes their perception of that waiting time is only a few minutes; however, after five minutes customer perception of their waiting time increases exponentially. Furthermore, a five-minute average waiting time results in only 2% of customers leaving. The manager wants to monitor speed of service using a statistical process control chart. At different times during the day over a period of several days the manager had an employee time customers' waiting times (from the time they entered an order line to the time they received their order) at random. There were 15 samples taken of size 6. The data is provided below.

1. Management wants customers to receive their orders within 5 minutes +/- 1 minute, and it has designed its ordering and food preparation process to meet that goal. Compute Cp and Cpk and indicate if the process is capable of meeting the restaurant's goal for speed of service. Is the process centered? Justify your answer(s).