title: How to divide $1 in preg_replace?
body: <p>I want to convert all sizes in a html document. Everything with **px should be divided by 4. So 100px would become 25px.</p>
  
  <p>For example:</p>
  
  <pre><code>&lt;div style="height:100px;"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>should become</p>
  
  <pre><code>&lt;div style="height:25px;"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>Here is a php code I wrote. But it doesn't work.</p>
  
  <pre><code>$content = "&lt;div style=\"height:100px;\"&gt;&lt;/div&gt;";
  $regex = "#([0-9]*)px#";
  $output = preg_replace($regex,"$1/4",$content);
  </code></pre>
  
  <p>How do I do?</p>