a: \(=\dfrac{\dfrac{8}{27}\cdot\dfrac{9}{16}\cdot\left(-1\right)}{\dfrac{4}{25}\cdot\dfrac{25}{144}}\)
\(=-\dfrac{72}{432}:\dfrac{4}{144}=-\dfrac{1}{6}\cdot36=-6\)
b: \(=\dfrac{3^6\cdot2^6+3^6\cdot2^3+3^6}{-73}=\dfrac{3^6\left(2^6+2^3+1\right)}{-73}=-3^6\)