The math
Required final score = (target grade − current grade × (1 − final weight)) ÷ final weight. For example: with an 87% current grade, a 90% target, and a 25%-weighted final, you need (90 − 87 × 0.75) ÷ 0.25 = 99% on the final.
What if the needed score is over 100%?
Then the target is mathematically impossible without extra credit. Lower your target or ask about extra-credit opportunities.
Does this work with weighted categories?
Yes — your "current grade" should already reflect your class's category weights. Only the final's weight goes in the third box.