Removing a Set In Stains From Clothing

Removing a Set In Stains From Clothing

I have three white shirts that have set in stains. One has a mysterious blue stain, the other a yellow stain (maybe oil of some sort), and the other has a small black grease stain. Anyone have a solution on how to remove them? Any help would be appreciated. There is nothing else wrong with the garments.

Erin from PA