Using non-literal strings in different methods in C#

Fine, here you go.

Passing the textbox values as arguments in the parameter.

public sealed partial class MainPage : Page
{
    public MainPage()
    {
        this.InitializeComponent();
        txtName.Text = "Your name";
        tbxAge.Text = "Your age";
        tbxDinner.Text = "Your dinner";
        OutputNewValues(txtName.Text, tbxAge.Text, tbxDinner.Text);
    }

    private void OutputNewValues(string name, string age, string dinner)
    {
        string answer = "Hello, " + name + " you are " + age + " years old. " + dinner + " sounds yummy for dinner!";
        finalOutput.Text = answer;
    }
}

or using member variables:

public sealed partial class MainPage : Page
{
    private string name = "Your name";
    private string age = "Your age";
    private string dinner = "Your dinner";
    public MainPage()
    {
        this.InitializeComponent();
        OutputNewValues();
    }

    private void OutputNewValues()
    {
        string answer = "Hello, " + name + " you are " + age + " years old. " + dinner + " sounds yummy for dinner!";
        finalOutput.Text = answer;
    }
}