A quality inspector took four samples, each with five observations, of the duration of a customer service at a station. The following table shows her observations in minutes. What is the three-sigma upper control limit for the sample mean?

Sample (in minutes)
#1	#2	#3	#4
12	10	11	12
13	12	13	14
12	13	12	18
15	16	15	13
16	15	17	14

		11.675
		14.005
		14.485
		16.840
		None of the above