If you have a spreadsheet in one of the levels, you can save it separately from the rest of the session.
When a spreadsheet is inserted it will have menus next to the level number. The Table menu has items that let you save the spreadsheet in different formats, as well as insert previously saved spreadsheets.
You can save a spreadsheet with the Table ▸ Save sheet as text menu item. If you select that, you will be prompted for a file name; you should choose a file name that ends in .tab. Once you save a spreadsheet, there will be a button to the right of the menus which use to save any changes you make. If you want to save the spreadsheet under a different name, use the Table ▸ Save as alternate filename menu entry.
You can save a spreadsheet in other formats. The Table ▸ Save as CSV menu item will save a spreadsheet in a comma-separated values file, and the Table ▸ Save as mathml menu item will save the spreadsheet in as a MathML file.
use the Table menu to insert previously saved spreadsheets; the menu item Table ▸ Insert will bring up a directory browser that use to select a file to enter.