write text on top of loaded box image right in the middle

I created a box in paint and loaded it onto sprite using

     [Embed(source="Colbox.png")]
     var Colbox:Class;
     private var NBVar:Bitmap = new Colbox ();

Code.The code that sets the coordinates

        txtFld.x = 100;
        txtFld.y = 100;
        txtFld.width = 300;
        txtFld.height = 300;
        txtFld.text开发者_运维百科 = "80";

        NBVar.x = 80;
        NBVar.y = 80;

        addChild(NBVar);
        addChild(txtFld);

However the number 80 does not appear in the middle of the colored box. Is there a easier method to achieve this with better accuracy ?

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NBVar.x = (colored_box.width/2) - (NBVar.width/2);
NBVar.y = (colored_box.height/2) - (NBVar.height/2);

This code will give u the perfect centre, and the NBVar should be the child of colored_box.