title: Take value of the child of a child of a child in Firebase
body: <p>I'm trying to observe this value:
  <a href="https://i.stack.imgur.com/ccAI8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ccAI8.png" alt="enter image description here"></a></p>
  
  <p>With this code:
  <a href="https://i.stack.imgur.com/yT6J6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yT6J6.png" alt="enter image description here"></a></p>
  
  <p>But this give me error. I tried many times with other database methods like make value1 in a single child divided by value 2.</p>