Explanation
3x is a multiple of 3; thus, adding 5 to that number yields a number that is not a multiple of 3. Choice (1) is incorrect because x > 0 and therefore must equal 3 or some multiple of 3. Choices (3), and (5), (6) are incorrect because any integer multiplied by 3 is a multiple of 3, and any multiple of 3 (such as 6 or 18) added to a multiple of 3 is also a multiple of 3.