How do I calculate my average in classes

I'm terrible at math, so that's why I'm asking (I don't need smart comments btw, everyone has a subject they're bad at)

My philosophy class:
Quizzes: are worth 20%
Journnals: are worth 20%
3 Exams: are worth 20% EACH
My quiz average is 97 (there are 20 quizzes total)
My exam average is 82 and that includes ONLY two exams so far.
My journal average is 100 (there are 12 journals total)

Plus, 15 points added to total average from extra credit.

(.2 * .97 + .82 * .4 + .2) / .8 =
.722 / .8 =
0.9025

90.25% not including your extra credit