function  cpufan(){
 if(document.myfrom.mybox6.checked==true)
     {
       var a12 = window.document.getElementById("cpufan_a12").value;
       var total = 12 * a12;
       window.document.getElementById("cpufan_total").value = total;
    }
  else
      {
       window.document.getElementById("cpufan_num").disabled=true;
       window.document.getElementById("cpufan_total").value = 1.25;
 }
}