How do I make a variable show up in a view?

I have a variable called End_Time, which is just the user input start time plus a duration.   I want to display this in a form, but the option is not showing up.  I would assume that I would be able to select this variable to show up under the Column Properties tab, but only the input fields from the form appear there.

So right now I have:

On Edit

   End_Time = Start_Time.addMinutes(input.Duration.toLong())

Thank you.