Tìm x, biết:

* Hướng dẫn giải

$\begin{array}{l}a)x=\frac{21}{55};\begin{array}{ccc}& & \end{array}b)x=\frac{-11}{26};\\ \\ c)x=\frac{11}{18};\begin{array}{ccc}& & \end{array}d)x=1\end{array}$

$\begin{array}{l}d)x=-1;\begin{array}{ccc}& & \end{array}e)x=\frac{11}{7};\\ \\ f)x=20\end{array}$