\[\boxed{\text{6.12.}}\]
\[\textbf{а)}\ 7\ :2 = \frac{7}{2} = 3\frac{1}{2};\ \]
\[\textbf{б)}\ 7\ :12 = \frac{7}{12};\ \]
\[\textbf{в)}\ 6\ :10 = \frac{6}{10} = \frac{3}{5};\ \]
\[\textbf{г)}\ 25\ :10 = \frac{25}{10} = \frac{5}{2} = 2\frac{1}{2}\text{.\ \ \ }\]