4. A process control chart shows the process average (mean) of 6.5 days from order receipt to order fulfillment with an average range of 1.6 days. The sample size is 4 orders. What is the upper control limit (UCL) and the lower control limit (LCL) for the process?

a. UCL = 7.67 days LCL = 5.33 days

b. UCL = 5.33 days LCL = 7.67 days

c. UCL = 8.10 days LCL = 4.90 days

d. UCL = 4.90 days LCL = 8.10 days