How to compute each user price?

hai every one i am new to emberjs .i want to compute user price if i suppose to enter 1 user i want to output price=$20 like that if i enter 2 users output price =$40 plz help me thanks

Like this:

price: Ember.computed('quantity', function() {
  return this.get('quantity') * 20;
})

thanks a lot @emberigniter i like yours posts so much in your emberinniter

could u plz help me how to create price switching label??