\[x^{3} - \left( 4x + x^{2} \right)(x - 4) =\]
\[= x^{3} - 4x^{2} - x^{3} + 16x + 4x^{2} =\]
\[= 16x;\]
\[x = \frac{1}{16}:\]
\[16 \cdot \frac{1}{16} = 1.\]