a) \(\dfrac{20^5.5^{10}}{100^5}=\dfrac{\left(20.5\right)^5.5^5}{100^5}=\dfrac{100^5.5^5}{100^5}=5^5\)
b) \(\dfrac{\left(0,9\right)^5}{\left(0,3\right)^6}=\dfrac{\left(0,3.3\right)^5}{\left(0,3\right)^6}=\dfrac{\left(0,3\right)^5.3^5}{\left(0,3\right)^6}=\dfrac{3^5}{0,3}=\dfrac{10.3^5}{3}=10.3^4=810\)