At a large retail store, a separate billing counter was made for customers that purchase just one item. A study found that the time taken by this counter for billing a single item had an average range of 12.3 seconds over a sample of 15 randomlychosen billings. An earlier time study had specified that the billing time for one item at this store ought to be between 48 and 56 seconds. If the process can be assumed to be in control, what is the sigma-level of the process (do not confuse with sigma, the standard deviation) (choose closest value)? A. 1.15 B. 3.40 C. 0.85 D. 2.70 E. 4.55