Find what grade you need on the final:
Current grade is 70% (or C-).
Final exam weight is 50%.
Required grade is 80% (or B-).
The final exam grade is equal to 100% times the required grade, minus 100% minus the final exam weight (w) times the current grade (g), divided by the final exam weight (w):
Final exam grade =
= ( required grade - (100% - w)×current grade ) / w
= ( 80% - (100% - 50%)×70% ) / 50% = 90%
So the final exam grade should be 90% (or A-).
Assigment 1: weight1=50%, grade1=16 out of 20.
Assigment 2: weight2=30%, max grade=30.
Assigment 3: weight3=20%, max grade=40.
Find average grade in assignments 2 and 3 needed to get class grade of 85%.
Current grade = Assignment 1 grade = grade1 / max grade1 = 16/20 = 0.8 = 80%
Required grade = 85%
Final exam weight = w = weight2+weight3 = 30%+20% = 50%
Final exam grade =
= ( required grade - (100% - w)×current grade ) / w
= ( 85% - 50%×80% ) / 50% = 90%
This mean that you have to get an average grade of 90% in assignments 2 and 3 in order to get class grade of 85%.
Assignment 2 grade = 90% × max grade = 90% × 30 = 27
Assignment 3 grade = 90% × max grade = 90% × 40 = 36