title: How to add an extra property into a serialized JSON string using json.net?
body: <p>I am using Json.net in my MVC 4 program.</p>
  
  <p>I have an object <code>item</code> of class <code>Item</code>. </p>
  
  <p>I did:
  <code>string j = JsonConvert.SerializeObject(item);</code></p>
  
  <p>Now I want to add an extra property, like <code>"feeClass" : "A"</code> into <code>j</code>. </p>
  
  <p>How can I use Json.net to achieve this?</p>