Final answer:
To count the number of account staff invoices that are 30 or more days past due in cell I6, use the COUNTIFS function with the criteria ">=30" and "account staff". For cell I7, to count the invoices with 'custom tax,' use COUNTIFS with "custom tax" as the only criterion.
Step-by-step explanation:
The involves using the COUNTIFS function in Microsoft Excel, which falls under Computers and Technology. This function is used to count the number of cells that meet multiple criteria. For cell I6, if you want to calculate the number of account staff invoices that are 30 or more days past due, you would use the formula =COUNTIFS(range, ">=30"), where 'range' is the range of cells containing the days past due. If the range of invoices is in column A and the status of the invoice is in column B, your formula would look something like =COUNTIFS(A:A, ">=30", B:B, "account staff"). For cell I7, if you want to count the invoices with a 'custom tax' status, suppose the tax status is in column C, the formula would be =COUNTIFS(C:C, "custom tax").