Also, another question that I've been asked: "How many exams should I do?"
This is question, I can't answer nor can anyone else. It really comes down to the individual. Some may only need to do 10 exams and feel prepared, others may feel the need to 30+ exams in preparation for the exam. There isn't a set value/number of exams which will get you a good score for Accounting, let alone any other subject. Do as many exams as you need, until you feel fully prepared!
If you want to know how many I did - for the Unit 3 exam, I did about 10~15 exams. For the Unit 4 exam, I did 20+ (close to 25) exams. Again, the amount of exams I did is irrelevant - that was the amount of exams I felt I needed to do, in order to be fully prepared. Doing more exams doesn't necessarily mean you'll do any better than someone who does 5 exams. It varies from person to person.