So, I just ended my high school finals and realize that in math I have a 78.9% and need a 79.5% for a B-, what should I do? How should i reason with my teacher? I doubt he'll just raise my grade or give me extra-credit.

This teacher ALREADY rounds up - A 75.5% rounds up to an 80%, which has been a B for most scales for quite a long time. When I was in h.s., many moons ago, a B was 84%, and the nuns wouldn't have even considered rounding up. Also, it's easier to get 80% than it used to be - this is grade inflation. Of course grading, in itself, is a whole separate subject for discussion. I'm a retired professor. Believe me when I tell you that grading was for me the LEAST pleasant aspect of teaching. I wanted to be generous but one MUST be fair.

Sorry, but since you obviously can do enough math to figure out percentages, you should have figured out what grade you needed a few weeks ago, when there was still an opportunity to do something about it--like study harder. Waiting until after the class is over doesn't seem like the best time to try and do something.

u should have studied!!

if you are struggling tell your teacher that you need a little help and ask if you can do extra work to bring your grade up. Good Luck!

If he won't raise your grade or give you a chance to earn extra credit, I don't see what can be done unless a mistake was made or you can present some reasonable explanation why your grade should be highter.