How to get the order of selected items from different comboBoxes

What do you mine by Line (Lets say that line 4 contains the value of item 3). What is a Line in this context?

First of all, why do wanted to get such reordering in first place? And what's the problem?
—SA

In your question you have clear answer.In each Combo Selected Index change call a function and pass your combo selected items and from file check for the combo selected item in each record and concatenate all the result and display the final result in your text box.

Are you saying the each of the four ComboBoxes contains unique entries for each of its Items ?

It's also important to clarify exactly whether you are adding instances of Objects (like instances of Classes) to the ComboBox's Item collection (where those Objects have the feature that 'ToString() is over-ridden, or they, in some way, return the string that the ComboBox needs to display for each item so that you can distinguish item from item. I'm going to assume, for now, that you are inserting instances of objects, not just strings.

Finally, you need to let us know how the TextBox, in which you want the selections in the ComboBoxes displayed, is updated: when the user presses a button, or automatically, or ... ?