(i) $\Big(-\dfrac{243}{32}\Big)^{-\dfrac{3}{5}}$

(ii) $\Big(5\dfrac{23}{64}\Big)^{-\dfrac{2}{3}}$

Simplify the following:

$\dfrac{a^{-1} + b^{-1}}{(ab)^{-1}}$

Simplify the following:

$\dfrac{x^{-1}y^{-1}}{x^{-1} + y^{-1}}$

Simplify the following:

$\dfrac{(4 \times 10^7)(6 \times 10^{-5})}{8 \times 10^{10}}$