Answer:
1. Excel file extensions, using XLS or XLSX, help him to save worksheets.
2. (Files) help Aslam to create multiple worksheets with common styles.
3. He needs to save them with the (xls).
Explanation:
The file extension (also called the filename extension) is the ending of a file that identifies the type of file in an operating system, for example, Microsoft Windows. The filename extension starts with a period, followed by one, two, three, or four characters, especially in Microsoft Windows. The filename extension helps the computer to open the correct program whenever one wants to use the file.