Unfortunately I am not really good at prepositions. I know a lot but of course not all. Sometimes it is totally clear but other times I can't decide it. I am thinking about it a lot. Trying to say them loud to decide which one sounds better, but I don't always choose the right one. That's why I ask for help. Sorry for annoying you.
In Hungarian we say sitting on the balcony, playing on the playground, working on the economic department, but it is not always the same in English. So it is difficult to choose.
:-(