\(\frac{45^{10}.5^{20}}{75^{15}}=\frac{\left(3^2.5\right)^{10}.5^{20}}{\left(3.5^2\right)^{15}}=\frac{3^{20}.5^{10}.5^{20}}{3^{15}.5^{30}}=\frac{3^{20}.5^{30}}{3^{15}.5^{30}}=3^5=243\)
\(\frac{\left(0,8\right)^5}{\left(0,4\right)^6}=\frac{\left(0,4.2\right)^5}{\left(0,4\right)^6}=\frac{\left(0,4\right)^5.2^5}{\left(0,4\right)^6}=\frac{2^5}{0,4}=\frac{32}{\frac{2}{5}}=32.\frac{5}{2}=80\)
\(\frac{2^{15}.9^4}{6^6.8^3}=\frac{2^{15}.\left(3^2\right)^4}{\left(2.3\right)^6.\left(2^3\right)^3}=\frac{2^{15}.3^8}{2^6.3^6.2^9}=\frac{2^{15}.3^8}{2^{15}.3^6}=3^2=9\)