1. Select the column of numbers that you want to modify.
2. Right-click on the selected cells and choose "Format Cells" from the drop-down menu.
3. In the "Format Cells" dialog box, select the "Custom" category.
4. In the "Type" field, enter the following format:
   Code:

   "B0"

   .
5. Click "OK" to apply the format to the selected cells.

This will add the letter "B" in front of every number in the selected column. The "0" in the format ensures that any leading zeros in the original number are preserved.