[A2A] I would just sleep well and do whatever I know in the exam. Many students make the mistake of night-outs before the exams which really brings down their efficiency and concentration. So, they can't even do the questions that they know.
Other than that, it entirely depends on the subject and the teacher, whether you should spend 6 hours on 1 chapter or 2 hours each on all 3 chapters. But, I think 6 hours is a long enough time to prepare all 3 chapters. Now, if you have never picked up the book prior to this, I don't know what advice to give you. I don't think I have ever been in this situation for an exam which I considered important.
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