\[m + n = 8;\ \ \ \ p = 3:\]
\[\frac{2 \cdot (m + n)}{m + n - 2p} = \frac{2 \cdot 8}{8 - 2 \cdot 3} =\]
\[= \frac{16}{8 - 6} = \frac{16}{2} = 8.\]