If you select the cell with the first example number, the Imput line (aka Formula bar) might show…
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In the cases 1 and 2, you could use a formula in a column next to the numbers: =NUMBERVALUE(REGEX(A1,"[()'-]","","g")), being A1 the cell with the value.
Also can select the cells, copy, paste in a text editor (Notepad, Gedit, TextEdit or the like); select all in the text editor, copy, and paste in the spreadsheet, wich will show a dialog box named Text Import: hitting OK should work.
More LibreOffice Help on NUMBERVALUE, REGEX.
In the case 3, you could:
- select the cells;
- choose menu
Format - Cell… (the same that Ctrl+1) - Numbers tab, and select Category Numbers and Format Standard - OK;
- choose menu
Edit - Find & Replace…, with - in Find:, leave Replace: empty, then press Replace All.
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Tested with LibreOffice 6.3.6.2 (x86); OS: Windows 6.1.