Generally speaking, the HSC mark that would be considered the bare minimum to have the slightest chance of being among the top 20 students in the state for Business Studies is 97. An HSC mark of 98 tends to be more common among students who place towards the 15-20th. For instance, in 2021, the student ranked 16th achieved an HSC mark of 98.
Of course, the higher the HSC mark from this point, the higher the chance of a student not only placing among the top 20, but they will also maximise their chance of achieving a higher state rank, i.e. placing higher among the top 20 students.
While being ranked first relative to the student's cohort is an important factor with respect to chances of achieving a state rank (this applies to all subjects), it is not the only requirement. Favourable performance is also crucial in the HSC exam, especially when considering that the Assessment Mark of a student ranked first relative to their cohort will be adjusted to equal the highest Examination Mark of any student in their cohort (recall the moderation process). Pursuing a state rank therefore calls the need for the student ranked first to also try to achieve the highest Examination Mark of their cohort, meaning that their own Examination Mark would become their HSC mark, which ultimately allows them to maximise their chances of a state rank.
I hope this helps!