Unable to execute multiple file in the project

[DarkEmperium]

So basically I having trouble to run this inheritance code during my lecture class, I did exactly the same thing on my pc and it work but in code app, it just won't work any solution for this ? Btw It just a simple inheritance code that link class to class

Sry that I'm not really familiar with this app so idk some of the functionality or what to do with this type of situation.