Hey Bina8,
Anyone can achieve any ATAR with any subject! : ) Many students achieve an ATAR of 80 and even 90+ with those subjects! : )
If you want to really know what marks you are aiming for go onto these two websites to break down what scores you should be aiming for. DO keep in mind that the ATAR calculators are different each year in terms of scaling and what percentile you're in - each canditure will have different results and from what I have heard 2017 was a strong cohort, so don't be too "Oh my gosh I can't do this!". The marks stated in the ATAR calculators should be used as a guide for you to have an aim for the HSC and to achieve your goals. : )
Also if you want to, talk to your teachers about what mark you should be aiming for the end of the year. If you're doing really well at the moment keep doing what you're doing. However, if you're struggling a bit with some of your subjects don't be afraid to ask for help! The best way to improve is send practice responses, papers (though for Maths/Science I think if you have a Success HSC One Past Paper book they will have answers with working out in them). Since you're a humanities girl like me send practice responses, don't forget to make notes and always use your teachers feedback to improve.
Here are the websites by the way:
http://www.matrix.edu.au/atar-calculator/ (go to Reverse ATAR - select the subjects your doing first then type in your goal ATAR).
https://talent-100.com.au/atar-calculator/#welcome (go to break down my ATAR)
All the best,
Gallen88
P.S. Please don't put too much pressure on yourself this year and do talk to someone if you are feeling stressed. It can be your parents, a teacher, a psychologist, a councellor, a friend, or your relatives. ( I noticed another post of yours stating you're suffering from mental health problems : ( - I hope you're feeling okay at the moment and are giving yourself some time to relax for your own mental health too.).