\[ \begin{align*} \dfrac{14}{21} \times \dfrac{35}{42} &= \dfrac{14\times 35}{21\times 42} \\ &= \dfrac{490}{882} \\ &= \dfrac{5}{9} \end{align*} \] \[ \begin{align*} 5 \times \dfrac{3}{7} \times \dfrac{14}{15} &= \dfrac{5\times 3\times 14}{1\times 7\times 15} \\ &= \dfrac{210}{105} \\ &= 2 \end{align*} \] \[ \begin{align*} \dfrac{8}{9} \times \dfrac{27}{12} \times \dfrac{4}{3} &= \dfrac{8\times 27\times 4}{9\times 12\times 3} \\ &= \dfrac{864}{324} \\ &= \dfrac{8}{3} \end{align*} \] \[ \begin{align*} \dfrac{2}{3} \times 6 \times \dfrac{5}{4} &= \dfrac{2\times 6\times 5}{3\times 1\times 4} \\ &= \dfrac{60}{12} \\ &= 5 \end{align*} \]