CSS - Hide elements (class) based on value of select box

Answer 1

I would use personally create another class for hidden objects (eg 'hiddenClass'), and use jquery similar to the following:

$( "#typeBox" ).change(function(){
 if($("#typeBox").val()=="other")
 {
     $(".applicableSupportCase").each(function(){
         $(this).addClass("hiddenClass");
     });
 }
});