C#

public struct Fun3ReturnValues
{
    public int SomeValue { get; set; }
    public string SomeOtherValue { get; set; }
}
...
public static Fun3ReturnValues Fun3(int y, int z)
{
    return new Fun3ReturnValues
    {
        SomeValue = 42,
        SomeOtherValue = "Hello",
    };
}

public struct EnteredText
{
 public string t1, t2, t3;
};

public partial class Form3 : Form
{
 public delegate void ButtonClick(EnteredText data);
 public event ButtonClick OnClick;
...
 private void buttonAddRow _Click(object sender, EventArgs e)
    {
        EnteredText args;
        args.t1 = textbox1.Text; args.t2 = ...
        if (OnClick != null)
            OnClick(args);
    }
}

 Form3 f3 = new Form3();
 f3.OnClick += f3_OnClick;
 f3.Show();
}
private void f3_OnClick(EnteredText txt)
{
// do something with the text or refire a new event.
}