"The correct answer is .xlsx. Key Points Microsoft Excel is an electronic spreadsheet that runs on a personal computer. Microsoft Excel 2007 is a version of Excel developed by Microsoft. Files created in MS Excel are known as Workbook. The extension used in MS Excel 2007 is '.xlsx' Additional Information"

=REPLACE(RIGHT(A1,5),1,SEARCH(".",RIGHT(A1,5)),"")

This formula wil be useful if you have more than one dot in filename

xlsExplanation:The XLS file extension is used for files saved as Microsoft Excel worksheets. Excel is a popular spreadsheet program used with data like numbers and formulas, text, and drawing shapes. Excel is part of the Microsoft Office Suite of software.

"The correct answer is the xlsx. Key Points The Microsoft Excel Binary File format, with the .xlsx extension and referred to as XLS or MS-XLS, was the default format used for spreadsheets in Excel through Microsoft Office 2003. The format is also referred to as Binary Interchange File Format (BIFF) in Microsoft's technical documentation. The default XML-based file format for Excel 2010 and Excel 2007. Cannot store Microsoft Visual Basic for Applications (VBA) macro code or Microsoft Office Excel 4.0 macro sheets (.xlm). Additional Information .xlsm The XML-based and macro-enabled file format for Excel 2016, Excel 2013, Excel 2010, and Excel 2007. Stores VBA macro code or Excel 4.0 macro sheets (.xlm). .xlsb The binary file format (BIFF12) for Excel 2010 and Excel 2007. .xltx The default file format for an Excel template for Excel 2010 and Excel 2007. Cannot store VBA macro code or Excel 4.0 macro sheets (.xlm). .xltm The macro-enabled file format for an Excel template Excel 2010 and Excel 2007. Stores VBA macro code or Excel 4.0 macro sheets (.xlm)."