\[a^{12} \cdot \left( a^{- 4} \right)^{4} = a^{12} \cdot a^{- 16} = a^{- 4};\]
\[a = - \frac{1}{2}:\]
\[\left( - \frac{1}{2} \right)^{- 4} = ( - 2)^{4} = 2^{4} = 16.\]