Упрости выражение

\(\left ( \dfrac{a}{a^2-16}-\dfrac{1}{a+4} \right ) : \dfrac{8a}{a^2+8a+16}-\dfrac{1}{a-4}=\) [ \(-\frac{1}{2a}\) | \(-\frac{1}{2a+1}\) | \(\frac{1}{2a}\) | \(-\frac{a}{a-4}\) ]