How to LisBox.ItemsSource to Textblock.Text

I send  from ListBox to TextBlock. (tLat to tLat1)
ListBox is show 13.765443 ,But TextBlock is show System.Windows.Control.ListBox.


List t_la = new List();
foreach (myList cm in list)
t_la.Add(cm.L_id);
tLat.ItemsSource = t_la;
               
tLat1.Text = tLat.ToString();