Questions I like help with

1. I am using the third edition from mike meyers and
the train signal training videos.
Both of these venhors are authorized with comptia to produce these study guides but give different information.
etc. Mike meyers study guides say WAP work on the physical layer.
FDDI has a maximum ring size of 100 kilometers.
Train signal say WAP work on the Data layer.
FDDI has a maximum ring size of 60 kilometers.
2. I understand that the pass score is 554 so how many questions can I get wrong out of the 85 questions for me to failed?
3. In the pratice test if you are unsure with an question you can mark it and go back to it later. Can you do this in the real test?