Can't run PHP site on VirtualBox. What is the problem?

Question

PHP

Ubuntu server 18.04
is installed on the virtual machine PHP 7.2
Apache2
MySQL is installed

The folder with the site is in /var/www/html/
When the site is launched, the browser gives such an error
in the list of mysql users, it shows this
Help to solve the error

Answer 1

Are you sure you have the correct password in your site config?

Answer 2

The problem is that you have not configured a connection to the database, or rather the wrong password.

Answer 3

look at the 23rd line in class_db.php and where it leads. This is the connection to the database. It's not configured