Thanks Jazz519. I agree, x^2, not x^3. Not sure what I did there, maybe I looked at the 3 coefficient for too long! Lol.
My answer to 12ei was 2/5. On the right, next to the question. I wrote 3/5 next to Odd on my tree diagram (which I didn't end up really looking at).
Thanks for checking it...
Exam:
http://educationstandards.nsw.edu.au/wps/portal/nesa/11-12/Understanding-the-curriculum/resources/hsc-exam-papers/hsc-exam-paper-detail/2017/mathematics-2017-hsc-exam-pack/
Solutions:
http://docdro.id/UB5mMFU
Enjoy!
Let me know if I have any mistakes too.