title: Add days to date in Laravel
body: <p>I am beginner in Laravel. I use in my project Laravel 5.8.</p>
  
  <p>I have this code:</p>
  
  <pre><code>$userPromotionDays = $user-&gt;premiumDate; // 2019.08.28
  $daysToAdd = 5
  </code></pre>
  
  <p>How can I add $userPromotionDays to $daysToAdd (in Laravel/Carbon)?</p>