Bài giải:

$\begin{align}& \frac{242}{363}+\frac{1616}{2121}=\frac{2}{7}\times A \\ & \frac{2\times 121}{3\times 121}+\frac{16\times 101}{21\times 101}=\frac{2}{7}\times A \\ & \frac{2}{3}+\frac{16}{21}=\frac{2}{7}\times A \\ & \frac{14}{21}+\frac{16}{21}=\frac{2}{7}\times A \\ & \frac{30}{21}=\frac{2}{7}\times A \\ & \frac{10}{7}=\frac{2}{7}\times A \\ & A=5 \\ \end{align}$