The program is very straightforward. It gets the contents or the source code of any specified php file and stores it in the variable lvl_text. As is evident only php files can be accessed. We need to get the contents of the file hackthissite.org/index.php. Now look at the URL of the mission.
We have traversed into two folders of hackthissite.org, i.e. missions and extbasic. So we need to go two folders backward. So we must enter
There is no need to add .php as it will be added by the program given.