For anyone good with percentages?

okay so in my college class quizzes are 20% of your grade and exams are 80%. I have a 90% average for all of my quizzes. I made a 79% on the first test and an 89% on the second test. What do i have to make on the third test to make an A in the class. also, if you could explain how you figured it out that would be greatly appreciated.