Final answer:
The formula =Sum (Quarterly sales[[#totals], [2017], [2018]]) adds up the total quarterly sales for both the years 2017 and 2018.
Step-by-step explanation:
The correct interpretation of the structured reference formula =Sum (Quarterly sales[[#totals], [2017], [2018]]) is that the formula calculates the sum of quarterly sales for the years 2017 and 2018. This formula is likely being used within a spreadsheet that utilizes structured referencing, which is a feature of some advanced spreadsheet programs like Microsoft Excel to work with table data more easily. Here, [#totals] refers to the total row of a table, while [2017] and [2018] refer to the specific columns for those years. The inclusion of both years in the formula indicates it will sum the totals of these two separate columns.