Here is a simple line of code you can use to find the web root and path of your website.
Copy and paste this code into a text file:
<?php print ($_SERVER['DOCUMENT_ROOT']); ?>
Save the file as findwebroot.php or whatever name you want, as long as it has a php extension.
Upload the file to your server, navigate to the file in a browser, and voilà - you will see the full path to that file!