a) $\frac{2^3.3^4}{2^2.3^2.5}$ = $\frac{2.3^2}{5}$ =$\frac{2.9}{5}$ =$\frac{18}{5}$
b)$\frac{1989 . 1990 + 3978}{ 1992 . 1991 - 3984}$ = $\frac{1989 . 1990 + 1989.2}{1992 . 1991 - 1992.2}$ =$\frac{1989.(1990+2)}{1992.(1991-2)}$ =$\frac{1989.1992}{1992.1989}$ =1
c) $\frac{121.75.130.169}{39.60.11.198}$= $\frac{11^2.3.5^2.2.5.13.13^2}{3.13.2^2.3.5.11.2.3^2.11}$ =$\frac{2.3.5^3.11^2.13^3}{2^3.3^4.5.11^2.13}$ = $\frac{5^2.13^2}{2^2.3^3}$ =$\frac{25.169}{4.27}$ =$\frac{4225}{108}$