You say you know that each term in the sequence is three times the previous term. That's great! Now let's see if we can use that one fact we know to discover another fact. We know the first term of the sequence is 2. That's not terribly helpful, but we'll note it down anyway. Maybe it'll come in handy for later. The second term is 6. Keeping in mind our rule of how the sequence is generated, we know that's the same as 2 * 3. Let's keep going. The third term is 6 * 3 = 18. But, hold on, we just found an expression for the second term. What happens if we plug that in? We find that the third term is (2 * 3) * 3 = 2 * (3 * 3) = 2 * 32. The fourth term is 18 * 3 = 54. Doing the same plug-n-chug as before shows that this is the same as (2 * 32) * 3. What's another way you can write that? Are you seeing a pattern emerging here? Can you create a similar expression for the fifth term? Does it fit your pattern?
People like to ascribe a lot of mysticism and weirdness to math, but really a great deal of math just boils down to critical thinking and pattern recognition. If you can successfully learn how to use what you know to find new information, and learn how to extrapolate patterns, that'll go a long way in just about any type of math. But most importantly, never be afraid to be wrong. If you've got a hunch, roll with it. If you think something might work, try it. Even in the worst case scenario where you fail, you'll almost always learn something and end up better off than you were before.
