The following samples have been taken from an on-going process. Use these values to create both an X bar and an R chart, and then answer the questions below.

Sample 1: 56 48 53 58 52

Sample 2: 50 59 57 54 54

Sample 3: 61 59 56 55 58

Sample 4: 57 51 46 57 50

Sample 5: 53 49 57 55 56

Sample 6: 56 55 60 58 56

What is the value of the centerline for an X bar chart?