\[\boxed{\mathbf{412}.}\]
\[\frac{48\ :4}{n\ :4} = \frac{m}{13}\]
\[\frac{12}{n\ :4} = \frac{m}{13}\]
\[m = 12.\]
\[n\ :4 = 13\]
\[n = 13 \cdot 4\]
\[n = 52.\]
\[Ответ:m = 12;\ \ n = 52.\]