Essentially your SAC ranking determines the SAC coursework score you obtain for your final combination of marks (used to rank and calculate study score).
If you are ranked 5th in SACs, you will inherit the 5th highest exam score as your coursework score. The coursework scores are moderated by VCAA by using the exam results, this ensures that schools with harder SACs but strong exam results are not disadvantaged. Then, for business management this moderated SAC score with make up 50% of your overall score, used to rank you for the study score (in combination with your personal exam score).
This is only my very basic understanding, hope I helped! As a very rough guide if you smash your exam and are in the top ~20% of your cohort going into it (SAC ranking) ,you should be a good shot for a 40+