Sample means and ranges were obtained for five samples of 10 units per sample from a production process. Assume the process was considered to be in control during the period these samples were collected. The results are as follows:

Sample Mean Range
1 10.58 0.23
2 9.97 0.25
3 9.99 0.21
4 10.23 0.28
5 10.23 0.28

Required:
What is the central line of the X chart for this process