Can i wear this for an mun conference? the dress code is formal to semi-formal but i’m worried it’s too unprofessional. it’s a red polo shirt, navy shirt and navy cardigan

That's great to wear! If you have an Iron, iron out the wrinkles. It'll look more formal, and you will be considered better-presented.

It depends on how it looks on you. The cardigan might not look professional enough but the rest would be fine. Maybe a blouse would be more appropriate or a blazer.

Show his work so he doesn’t get points taken off. this is because even if he can do calculations in his head, he may make a mistake and having it on the paper will not only him find mistakes but show that he was doing the work as well.