a) $0,(8)=8.0,(1)=8.\dfrac{1}{9}=\dfrac{8}{9}$
b) $3,(5)=3+0,(5)=3+(5.0,(1))=3+(5.\dfrac{1}{9})=3+\dfrac{5}{9}=\dfrac{32}{9}$
c) $0,11(7)=\dfrac{117-11}{900}=\dfrac{106}{900}=\dfrac{53}{450}$
d) $2,3(6)=2+0,3(6)=2+\dfrac{36-3}{90}=2+\dfrac{33}{90}=\dfrac{71}{30}$