Some functions also have optional arguments, which are enclosed in [square brackets] in the formula's syntax.
A formula must contain all of the required arguments, otherwise Excel displays ".
When using a number in an Excel formula, don't add any decimal separator or currency sign like $ or €.
For example, in North America you would write ) and check what character is set as List Separator there.
And then, use exactly that character to separate arguments in your Excel formulas.
If that doesn't work, you might have to create a new column, manually input the data (e.g.
copy your text-numbers to Notepad, and then back to a new column), and delete the broken column.