$$\\\left(\frac{1}{16}\right)^{-3/2}\\\\
=\left(\frac{16}{1}\right)^{3/2}\\\\
=16^{3/2}\\\\
=(16^{1/2})^3\\\\
=4^3\\\\
=64$$
If you want to understand more, look here.
http://web2.0calc.com/questions/indices-especially-negative-indices
$$\\\left(\frac{1}{16}\right)^{-3/2}\\\\
=\left(\frac{16}{1}\right)^{3/2}\\\\
=16^{3/2}\\\\
=(16^{1/2})^3\\\\
=4^3\\\\
=64$$
If you want to understand more, look here.
http://web2.0calc.com/questions/indices-especially-negative-indices