Analyze ad watch-time with Excel pivots

You are given a flat file with these columns: Date (Excel date, no time zone), UserID, AdID, WatchSeconds (integer ≥ 0), Clicks (integer ≥ 0). Using only Excel (no Power Query), do all of the following precisely: (1) Add helper columns to the source data: Weekday = WEEKDAY([@Date], 2) where Monday=1; ISOWeek = ISOWEEKNUM([@Date]); ISOYear = YEAR([@Date] + 4 - WEEKDAY([@Date], 2)). Explain why ISOYear is required at year boundaries. (2) Build a PivotTable to identify the single calendar date whose Clicks per watch-minute is highest. The ratio must be computed as (SUM Clicks) / (SUM WatchSeconds / 60) using a PivotTable Calculated Field (provide the exact field formula string). Resolve ties by choosing the earliest Date and describe how you’d enforce this tie-break deterministically in Excel. (3) Build a second PivotTable that aggregates total WatchSeconds by ISOYear and ISOWeek and returns the week with the maximum total WatchSeconds. If two weeks tie, pick the later week (by ISOYear then ISOWeek). (4) List two pitfalls that could produce wrong answers when using WEEKNUM/WEEKDAY versus ISO week logic (e.g., weeks spanning Dec/Jan, localized week starts). Output the two answers: the Top Date and the Top ISO week (as ISOYear-W##), and outline, step-by-step, the exact clicks/watch-minute and total WatchSeconds computations you would perform in the PivotTables.