Question 761887
You have to start with 3 (which is the first number) and go through multiples of 3 between 1 and 45, but ignore the multiples of 6 - since only odd numbers are given. (Multiples of 6 would be even).

Hence the 6th number in the list is 33 (choice c).

By the way, it is also the only *odd* number in the 4 choices, so should be able to guess that it is the right answer anyway :)