Tìm x, biết

Tìm x, biết:
$$\begin{gathered} a) x-\frac{20}{11.13}-\frac{20}{13.15}-\frac{20}{15.17}-...-\frac{20}{53.55}=\frac{3}{11} \\ b)\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+...+\frac{2}{x(x+1)}=\frac{2}{9} (x\in N^{*}) \\ c)\frac{3}{2}x-70\frac{10}{11}:\left(\frac{131313}{151515}+\frac{131313}{353535}+\frac{131313}{636363}+\frac{131313}{999999}\right)= -5 \\ d)\left(\frac{1}{1.101}+\frac{1}{2.102}+...+\frac{1}{10.110}\right).x=\frac{1}{1.11}+\frac{1}{2.12}+...+\frac{1}{100.110} \end{gathered}$$