HSC help failing one subject ?

so i have 11 units in HSC im getting 80's in all my subjects. however the only thing im failing is ancient history. im aiming to get in the 70's not really fussed or anything. Ancient history is the most hardest subject ever in year 12 with a lot of content and it gets really confusing. if say i end up failing my ancient history exam badly for my trails and HSC could i still end up with 70? i know this guy and he failed two exams and he got 60.