Need help: not working code

i have a select tag and in jstl im iterating values from a controller from database,,why is the below code not working,yung first nagana siya,but for the second hindi na,,i have an input id named commision and want to make its readonly to false,,,need help
#js
#jstl
#jsp
$("#Department").change(function(){
//working
if($('#Department option:selected').val() == 'Administration'){
alert(12);
}
//not working
if($('#Department option:selected').val() == 'Sales'){
$('#comission').attr('readonly', false)
}
});