Type your current overall grade, the final grade you are aiming for and the percentage of the course the final exam is worth. The required exam mark appears instantly along with the best and worst grades still possible.
Required final mark equals your target grade minus your current grade times one minus the exam weight, all divided by the exam weight. In plain terms it works out how much of the gap the exam alone has to close.
That means the target is no longer reachable with the exam weight you entered, even with a perfect paper. The tool says so directly and also shows the best possible final grade you can still achieve.
That is good news: you have already secured your target and would still reach it even if you scored nothing on the final. The tool shows the minimum mark as zero and tells you the grade you are guaranteed.