\[\frac{c^{2} - 10c + 25}{2c + 4} \cdot \frac{4c + 8}{c^{2} - 25} =\]
\[= \frac{(c - 5)^{2} \cdot 4 \cdot (c + 2)}{2 \cdot (c + 2)(c - 5)(c + 5)} = \frac{2 \cdot (c - 5)}{c + 5}\]
\[При\ c = 7,5:\]
\[\frac{2 \cdot (7,5 - 5)}{7,5 + 5} = \frac{2 \cdot 2,5}{12,5} = \frac{2}{5} = 0,4.\]