Final answer:
To determine the average number of years customers have been with Cello Worldwide, use the AVERAGE function in Excel.
Step-by-step explanation:
To determine the average number of years customers have been with Cello Worldwide, you can use the AVERAGE function in Excel. In cell M5, you can enter the formula: =AVERAGE(range).
Replace 'range' with the cell range that contains the number of years for each customer.
For example, if the years are in cells A1 to A752, the formula would be: =AVERAGE(A1:A752).