Every exercice asked has been put in a method to avoid polluting the code. You simply have to run one of the methods to get the asked exercice. This make possible to send only one file per exercice instead of have 2-3 files for one exercice.

About exercice 1.3, I understood the question as a graph of the total amoung of student per year. I don't know if you wanted the total amoung of student in each orientation facing the total amoung of students, but as you said I could do it as I understand it I did it this way.