Check to see if you can skip questions and come back to them. I don't know how "difficulty" is measured. Sounds like the questions are in "sections" so you get all "addition" for example and the addition problems get progressively more difficult so they can judge how "far" you have studied in that subject. I don't see how they could mix subjects/focus though, you might have learned addition but not multiplication so asking you a "harder" multiplication question after you did well in addition doesn't make sense.

But still, I'd think difficulty is a little bit subjective; my difficulty might be your piece of cake.

I'd check the statistics of answering a question versus time; if you skip a question it might be marked wrong but if you take a long time to answer the question, you might run out of time in the end. So at the start, check to see how many questions there are and divide by 120 minutes to see how long to spend per question. It could be though that skipping a question does not make it wrong but just gives you that many fewer total questions so your percentage correct/incorrect would change; that could make a difference if you get 10 wrong out of 100 or 10 wrong out of 90. So if you think you have a good chance answering a question (right or wrong) you might want to do so, just to keep your total up as getting it wrong might not damage you as much as skipping it could if you skip too many.