Question 176317
The sequence could possibly be 3, 6, 9, 27, 12, 15, ...  Notice how we add 3 to each term.



However, the sequence could also be 3, 6, 12, 24, 48, 96... Here we're multiplying  each term by 2. 



Or, you could multiply the each term by 3 and subtract 3. So 3*3-3=9-3=6



There are countless (possibly infinite) other ways to generate 3,6 ...



So there isn't enough information to determine the sequence given 3,6 ...