Showing result of in, esle statement in box

How do I show the answer to this in a box??

 

function multiply()
   {
  if(total < 10000)
  {
   commission = total * 0.001;
  }
  else
  {
   commission = total* 0.0008;
  }
   if (commission<5) commission =5;
   
   var total_commission =commission + total;
      document.getElementById("commission").value = total_commission;
 }