We are given the following sequence:
[tex]3,6,12,24[/tex]We notice that each term is found by multiplying the previous by 2, that is:
[tex]\begin{gathered} 3\times2=6 \\ 6\times2=12 \\ 12\times2=24 \end{gathered}[/tex]Therefore, this is a geometric sequence with a common ratio of 2.