The circumference of a circle is given by the formula
[tex]s=2\cdot\pi\cdot r[/tex]however we also knos that the diameter can be written as
[tex]D=2\cdot r[/tex]meaning that the formula for the circumference can also be written as
[tex]s=D\cdot\pi[/tex]then the circumference for the given information is:
[tex]\begin{gathered} s=12\cdot3.14 \\ s=37.68 \end{gathered}[/tex]