Ta có: \(71+\left(65\times4\right)=\frac{y+140}{y+260}\)
\(\Leftrightarrow331=\frac{y+140}{y+260}\)
\(\Leftrightarrow331\left(y+260\right)=y+140\)
\(\Leftrightarrow331y+86060=y+140\)
\(\Leftrightarrow331y-y=140-86060\)
\(\Leftrightarrow330y=-85920\)
\(\Leftrightarrow y=\frac{-85920}{330}=\frac{-2864}{11}\)