1. SQL / DATA STRUCTURES The SQL Commands are in the data.sql file. These will create the database and tables and also insert rows in them.

2. I have written the procedural function in index.php

3. I have completed the functions in universe.php. You can run it on any server.

4. $res = preg_replace("/[^0-9.\-]/", "", $val); This expression will remove all characters from a string except numbers.

5. The jquery exercise has been solved in jquery_exercise.php

6. The phpoffice/phpspreadsheet is the best library for PHP Excel work. It is very popular among PHP Developers. Has around 61 million installs. Very easy to install with composer. It has good tutorials and documentation. The Repo is here - https://github.com/PHPOffice/PhpSpreadsheet
   And a tutorial is here - https://www.webslesson.info/2020/03/phpspreadsheet-beginner-tutorial.html