a)$\frac{3.7.8.13}{14.15.26}$
=$\frac{3.7.8.13}{7.2.3.5.2.13}$
=$\frac{8}{2.2.5}$
=$\frac{8}{4.5}$
=$\frac{8}{20}$
=$\frac{2}{5}$
b) $\frac{11.8-11.3}{17-6}$
=$\frac{11.(8-3)}{11}$
=$\frac{11.5}{11}$
=$\frac{5}{1}$
=5
c)$\frac{17.13+17.2}{11.2-11.19}$
=$\frac{17.(13+2)}{11.(2-19)}$
=$\frac{17.15}{11.(-17)}$
=$\frac{(-1).15}{11}$
=$\frac{-15}{11}$