Range control limits

A quality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are in control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results:

Machine

#1

17

15

15

17

#2

16

25

18

25

#3

23

24

23

22

Using the above data and the factor table below, please answer the following questions.