The sample values in the table represent service times in minutes. Question: For the R-chart, what is the value of the upper control limit (UCL) (rounded to two spaces after the decimal)?

	Observation Number
Sample	1	2	3	4
1	10.1	10.6	9.8	9.9
2	9.7	9.5	10.3	10.5
3	10.1	10.7	9.2	10
4	9.9	9.8	10.4	10.1
5	10.4	10.1	10.9	9.9

The control charts constant chart is given below:

Sample Size (n)	Factor for X-bar (A2)	Factor for LCL for R (D3)	Factor for UCL for R (D4)
				2	1.88	0	3.267
3	1.023	0	2.574
4	0.729	0	2.282
5	0.577	0	2.114
6	0.483	0	2.004
7	0.419	0.076	1.924
8	0.373	0.136	1.864
9	0.337	0.184	1.816

Group of answer choices

a. 0.81

b. 2.57

c. 2.07

d. 2.24