title: Calculate the facebook cover offset y
body: <p>I'm getting the user cover photo using Facebook SDK. I have the path to the img and the offset y.</p>
  
  <pre><code>  "source": "http://a5.sphotos.ak.fbcdn.net/hphotos-ak-ash3/526114_459046674110601_992101492_n.jpg",
    "offset_y": 19
  </code></pre>
  
  <p>The div where i put the image have 300px height; and right background position is <code>center -146px;</code>. How to calculate the <code>top value</code> when I have 300 and 19 ?</p>