As the error says you cannot change inserted. Table Calcul will already contain rows submitted by insert at the moment trigger is called; therefore you operate directly on that data. As there is a possibility of inserting multiple rows at once, you should not work with local variables but work on a set.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.