$a){12}^{-4}:4^{-4}={\left(12:4\right)}^{-4}=3^{-4}$

$b){28}^{-7}:{14}^{-7}={\left(28:14\right)}^{-7}=2^{-7}$

$c){\left(-16\right)}^{-3}:{\left(-8\right)}^{-3}={\left(-16:\left(-8\right)\right)}^{-3}=2^{-3}$

$d){60}^{-2}:{\left(-15\right)}^{-2}={\left(60:\left(-15\right)\right)}^{-2}={\left(-4\right)}^{-2}$

$e)2^{-6}\cdot 5^{-6}={\left(2\cdot 5\right)}^{-6}={10}^{-6}$

$f)3^{-2}\cdot 2^{-2}={\left(3\cdot 2\right)}^{-2}=6^{-2}$

$g){\left(-4\right)}^{-3}\cdot {\left(-3\right)}^{-3}={\left(-4\cdot \left(-3\right)\right)}^{-3}={12}^{-3}$

$h){20}^{-3}\cdot {25}^{-3}={\left(20\cdot 25\right)}^{-3}={500}^{-3}$