How to get distance from raycast.

I updated my code, and the mousePos.z is still passed as 0.0. The raycast is working, as I already got results from the log. But this still isn't working.

 function Update () {
       
       //RayCast
       var hit:RaycastHit;
       var fwd = transform.TransformDirection (Vector3.forward);
       //var mousePos = Input.mousePosition;
       //var objectPos = Camera.main.ScreenToWorldPoint(mousePos);
       
       
       
           if (Physics.Raycast (transform.position, fwd, 15)) {
             var distance = hit.distance;
         }
       
       
       
       
       //Grass Block
       if(BlockID == 0){
       
         if (Input.GetButtonDown ("Fire1")) {
             
             //var fwd = transform.TransformDirection (Vector3.forward);
             
             var mousePos = Input.mousePosition;
            
             //mousePos.z = Physics.Raycast (transform.position, fwd, hit.distance);
             //mousePos.z = 3;
              mousePos.z = distance;
      
             var objectPos = Camera.main.ScreenToWorldPoint(mousePos);
             Instantiate(GrassBlock, objectPos, Quaternion.identity);
         }
     }