Question 945397
For the average of 3 grades to be an A ( 90 or above) the sum of the grades must be at least 3(90)=270. Current grades are 89+83=172 and 270-172=98, so your grade on the final must be 98 or better for a minimum 90 average. However if the average of the 3 grades falls below 80 (the sum of the grades <3(80) or 240) then you will receive a C.  the sum of your current grades is 172 So since 240-172=68 if your grade on the final is below 68 points, you will receive a C.
  SUMMARY you must score 98 or better on the final to receive an A in the course,
a score of 68 to 98 retains the B, but a score below  68 will lower your grade to a C.