Answer
$\frac{b(ab-16)}{a^2b^2-16}$
Work Step by Step
Multiply $\frac{b^2}{b^2}$ to the expression, we have:
$\frac{a-16b^{-1}}{(a+4b^{-1})(a-4b^{-1})}=\frac{b^2}{b^2}\cdot\frac{a-16b^{-1}}{(a+4b^{-1})(a-4b^{-1})}=\frac{b(ab-16)}{(ab+4)(ab-4)}=\frac{b(ab-16)}{a^2b^2-16}$
