Question 879361
You need an average of 80 in the class.
Let's say there are 2000 points in the class (that makes it easy because then your final is worth 300 and there are 1700 points already earned.)
You have already earned .91 * 1700, or 1547 points.
You need .80 * 2000, or 1600 points.
That means, you only need 53 points out of 300 on the final, or 17{{{2/3}}}%.  Breathe easy!  15 questions correct will put you over.