A quality engineer at Lockheed Martin is required as a part of ISO AS9100 certification to check the tolerances on all aerospace components every hour. The Quality Assurance team utilizes x-bar and R-charts to monitor the process. Eight times throughout the course of a shift, the quality engineer collects four samples (n=4) from a manufacturing line for inspection. The data collected by the engineer for this part is as follows:

	Mean (mm)	Range (mm)
Group 1	12.01	0.4
Group 2	13.28	0.6
Group 3	14.01	0.2
Group 4	13.99	0.5
Group 5	14.13	0.6
Group 6	13.73	0.3
Group 7	14.42	0.8
Group 8	13.97	0.4

What is the X-bar Upper Control Limit (UCL_x)?

a. 14.24

b. 14.036

c. 13.965

d. 13.79