Excel Margin Formula Setup

I have an existing spreadsheet and I need you to build a clean, reusable formula that adds a percentage-based margin across several columns at once. The goal is simple: each product cost already in the sheet should automatically display its selling price after the margin is applied, and any future rows I add must calculate correctly without extra work on my part.

You’ll receive the workbook as it is now, along with the exact percentage I use. Please set up the formulas (or structured table columns, if that’s the most robust route) and test them so I can drop in new cost figures and instantly see the margin-adjusted numbers in every specified column.

Deliverables:
• Updated Excel file with the margin formula in place for all required columns
• A brief note or comment inside the sheet explaining how the formula works and where to edit the margin percentage later

That’s it—once the sheet is working flawlessly, we’re done.