Question 459148
Not enough info.
Depends on what value is put on the final and how much the class work is worth.
The final could be worth 50 % or 90%
You have an 81% in the class what is the lowest grade you could earn on the final and still keep your 81% in the class?
The writer says:

well the final is worth 15% of your grade hw is worth 30% quizes are worth 15% and tests 40%
Assuming that you mean that you have 81% average on hw, quizzes and tests.
.30*81+.15*81+.4*81+.15f=81
f=81 
To keep 81 you will need at least 81 on the final.