a)

$\frac{{27}^4\cdot 9^7}{3^{18}:{81}^3}=\frac{{\left(3^3\right)}^4\cdot {\left(3^2\right)}^7}{3^{18}:{\left(3^4\right)}^3}=$   $\frac{3^{12}\cdot 3^{14}}{3^{18}:3^{12}}=$