Let TextBox stretch to fill width in StackPanel

Question

I have a StackPanel in my WinRT C# Metro app that I want to use as container for a label/value pair (TextBlock and TextBox) like this:

Answer 1

I walked thru this desert for 10 minutes or hours, and figured out that the best native control to neast the contents is the grid look at my snipet that works fine:

this will generate a nice adaptable layout with a textbox steching and a butoon on it side that maintains his aspect