\[\frac{x^{3} \cdot x^{23}}{\left( - x^{4} \right)^{7}} = \frac{x^{26}}{- x^{28}} = - \frac{1}{x^{2}};\]
\[x = \frac{1}{5}:\]
\[- 1\ :\left( \frac{1}{5} \right)^{2} = - 1\ :\frac{1}{25} =\]
\[= - 1 \cdot 25 = - 25.\]