The XYZ company receives several complaints every day about the behavior of its truck driver. Over 15 days the owner recorded the number of calls to be 6, 4, 0, 2, 0, 3, 0, 8, 9, 6, 7, 4, 9, 5, and 8. Approximately, what is the upper control limit for the 3-sigma c-chart?

Select one:

a. negative 10 and since a control limit cannot be negative round up to 0.

b. 9.03

c. 11.27

d. 13.00

e. 11.71