\[\boxed{\mathbf{37.}}\]
\[6\ :2 = 3\]
\[8\ :2 = 4\]
\[12\ :2 = 6\]
\[18\ :2 = 9\]
\[9\ :3 = 3\]
\[12\ :3 = 4\]
\[15\ :3 = 5\]
\[21\ :3 = 7\]
\[16\ :4 = 4\]
\[12\ :4 = 3\]
\[20\ :4 = 5\]
\[28\ :4 = 7\]