Launch Microsoft Office Excel 2007 and open the spreadsheet that you wish to save in CSV format. Use the "Ctrl-O" keyboard shortcut to open the file faster.

Open the spreadsheet in Excel, click "File" and select "Save As." Choose the first "Excel Workbook" option to save the spreadsheet with an .xlsx extension.

How to export Apple Numbers files as Microsoft Excel spreadsheets If you’ve been working in Numbers and will eventually return to Excel, you can export your spreadsheet as an Excel file.