(1st MP x 0.4) + (2nd MP x 0.4) = something.
desired final grade – something = G
G / .2
= what you need on your final exam.
In other words, multiply first marking period grade by 0.4.
Multiply second marking period grade by 0.4.
Add those two together (something).
Decide what you want your course grade to be (like 90 percent for an A in the course).
Subtract the “something” from the course grade you want.
Divide that by 0.2 and that’s what you need to get on your final.