php include error not findind the path

Your path to that file is obviously incorrect. This commonly happens when you use a relative path to a file and then start placing files in different directories. You should use the full system path to the file to avoid this issue:

include("/path/from/root/to/inc/db.php"); 

A common thing to do is define a variable or constant that defines the root path to your web files. That way if it ever changes (i.e. you change hosts) you only need to change it in one place.

In your config file:

define('ROOT_PATH', '/path/from/root/to/');

In your PHP files;

include(ROOT_PATH . "inc/db.php");