If I understand properly you must answer one of three questions in section 1 and also one of three in section 2. You want to know what the propbability is of none of the three questions in section 1 or none of the three in section two being among the 5 topics you studied, right?
If we assume that the topics are randomly selected, the chance that none of the three questions in section 1 are among the 5 you studied is (4/9)^3 = 8.8%. Since you must suceed on both sections 1 and 2, the chance of suceeding on both is (1-0.088)^2 = 83% if the topics are randomly selected. Hence the chanec of failing the exam is 1 - 0.83 = 17%
However, I suspect that the topics aren't random - I wouldn't expect that two or even all three questions could be on the samed topic, right? If this is true then the chance of all three questions on section 1 not being among the five is (4/9 x 3/ 8 x 2/7 ) = 4.7%. If it's required that all 6 questions be on 6 different topics then you are gurarranteed to get one section correct (because out of 6 questions at least 2 must be from topics you've covered). So you will fail if you fail section 1 or if you fail section 2. That probability is twice what we determined earlier, or 9.4%.
As you can see it makes a big difference whether topics may be repeated or not.