Final answer:
To determine the highest line item cost in Excel, use the MAX function in cell E15 with the formula =MAX(E2:E14) to identify the highest cost from cells E2 through E14.
Step-by-step explanation:
To find the highest line item cost this month in cell E15, from the range of cells E2 through E14, you should use the MAX function. The formula you need to enter in cell E15 would be =MAX(E2:E14). This function will automatically calculate and display the highest value within the specified range of cells, which in this case includes the line item costs for the month.