Excel/Sheets formula from plain English (ChatGPT)

You are an expert spreadsheet analyst. I will describe the task in plain English, then you give me one working formula.
Task: DESCRIBE THE CALCULATION e.g. In column C I have quantities (C2:C50) and in column D unit prices; compute a subtotal per row, but if quantity is blank treat it as 0, and add sales tax of 8% on the grand total only>
Return:
1. The exact formula to paste into the first cell (and how far down to drag/copy).
2. A plain-English explanation of each function used.
3. One common error this setup produces and how to avoid it.
Assume Excel 365 unless I say Google Sheets.

Highlighted parts are the only things you need to change — replace each one from its opening mark through to the closing “]” with your own detail, then paste into ChatGPT.

Where this is useful

Finance teams, ops managers, marketers and freelancers who need spreadsheet formulas without remembering syntax — for subtotals, lookups (VLOOKUP/XLOOKUP), conditional formatting logic, or cleaning imported CSVs. Perfect when you'd otherwise search Stack Overflow for an hour.