How do I save a LibreOffice Calc file for opening in Excel?
Solution 1:
Menu>File>Save As type ".xls".
Solution 2:
Open your spreadsheet in LibreOffice Calc. Navigate to File -> Save As.
Make sure you open the "File Type" menu:
Then either select .xls or .xlsx depending on whether the version of Excel you are using is 2007 or newer:
Click "Save" and there you go.