[Interest] QLineEdit "stretch" in QHBoxLayout using designer

[Carl Schumann]

Qt community,

I using Qt Designer to layout a very simple GUI via the following steps:
1. Using the "New Form" dialog I create a "Main Window"
2. Then a drop a Spin Box and a Line Edit widget onto the main window 
with the Line Edit to the right of the Spin Box.
3. Select both and then select Form -> Lay Out Horizontally from the 
main menu of Designer
4. Then try out the GUI with Form -> Preview ... from the main menu

The Line Edit has a fixed width that does not respond to resizing the 
main window or entering long text.   How do I make the Line Edit stretch 
to use up all the empty space to its right in the main window please?   
Thanks for any help.

Sincerely,
Carl Schumann