70.5/91 was an A+ for mid years last year, 74/90 for end of year.
wait, how did you work that out? :S
The first page in the link above is for "WRITTEN EXAMINATION 1", i.e. exam 1.
Now in the bottom row of the first table there is "Score Ranges". For an A+ the score range is 141-182, with a maximum of 182.
Now when it comes to VCAA exams,
two assesors mark them each giving a mark out of the total on the exam, hence why the total score in the link is 182, where as on the exam the total score will say

. So to achieve an A+ you need to get

, so 70.5 out of 91.
Same goes for the end of year, just go to the third page in that link ("Graded Assessment 3 WRITTEN EXAMINATION 2"), and pick the right numbers and divide by 2.