To add a footnote number at the end of a sentence in Microsoft Excel, follow these steps:

1. Click on the cell where you want to add the footnote.
2. Type the text that you want to appear in the cell.
3. Place the cursor at the end of the text where you want to add the footnote number.
4. Click on the "Insert" tab in the ribbon at the top of the screen.
5. Click on the "Symbol" button in the "Text" group.
6. In the "Symbol" dialog box, select "Latin-1 Supplement" from the "Subset" drop-down list.
7. Scroll down until you find the footnote symbol (it looks like a small number raised higher than the rest of the text).
8. Click on the footnote symbol to select it, and then click on the "Insert" button.
9. The footnote symbol will now appear at the end of the text in the cell.
10. To add the actual footnote text, click on the "References" tab in the ribbon at the top of the screen.
11. Click on the "Insert Footnote" button in the "Footnotes" group.
12. Type the footnote text in the footnote area at the bottom of the screen.
13. The footnote number in the cell will automatically update to match the number of the footnote text.

That's it! You now have a footnote number at the end of your sentence in Microsoft Excel.