If water is flowing through a pipe with diameter $\mathrm{}$d$1=12$  cm at $\mathrm{}$v$1=3\mathrm{.}0$  m$/$s $$and then moves into a new pipe and begins to flow at $9\mathrm{.}0$  $$m$/$s $,$ what is the diameter of the new pipe? Express your answer with the appropriate units.