How to add and keep score in every level?

Hello all, I'm a PhD student and I'm doing a simple game of collecting coins for my research. The question might be silly but I'm not a programmer. I'm trying to keep and add score in every level, but when the new scene is loaded the score starts again from the zero. My code so far is:

        static var score=0; var guiScore :
        GUIText;
        
        function start () { 
        guiScore.text = "Coins: "+score;
        }
        
        function OnTriggerEnter (other :Collider ) 
       { 
       Debug.Log ("OnTriggerEnter () was called"); 
       if (other.tag == "Coin") { 
       Debug.Log ("Other object is coin");      
       score ++;      
       Debug.Log
       ("Score is now " + score);
       Destroy (other.gameObject);      
       guiScore.text = "Coins : " +score; 
       Timer.onpause = true;      
       Application.LoadLevel("Menu2");      

} }

I would really appreciate any help. Thanks in advance.