Crucible and Cover + M of Magnesium Ribbon = ? Lab questions.?

So I'm doing this lab in chemistry and my teacher is horrible and wouldn't let me and my partner measure out the final result. We had to put magnesium ribbon in a crucible and cover and heat it until it becomes magnesium oxide. The m of the crucible and cover was 25.26 g and the m of the magnesium ribbon was O.51 g, should the m of crucible/cover/magnesium oxide equal the m of the crucible and cover plus the magnesium ribbon or something else? If you could give me an estimate that would be great. Like I said, my teacher is awful and I'd rather not curse about her here haha. Thank you :)