Here is the answer based on the given information above.
It is already given that 9 passengers do not have a frequent flyer account, and 1/3 of the next 30 has a frequent flyer account. 1/3 of 30 is 10. This means that out of the next 30 passengers, 10 have a frequent flyer account. The total number of passengers is 39. We have to find how many percent is 10 from 39. So we divide 10 by 39 and we get 0.26 and multiply this by 100 and we get 26%. Hope this answers your question.