(Tính :)

$\left( \frac{3}{7}\times \frac{11}{15}+\frac{3}{7}\times \frac{4}{15} \right):\left( 15+\frac{6}{11}-\frac{160}{11} \right)$=?

 $\begin{align}

  & =\frac{3}{7}\times \left( \frac{11}{15}+\frac{4}{15} \right):\left( \frac{165+6-160}{11} \right) \\

 & =\left( \frac{3}{7}\times 1 \right):\frac{11}{11} \\

 & =\frac{3}{7}\times 1\times \frac{11}{11}=\frac{3}{7} \\

\end{align}$