I don't know if this explains why but... it's because the answer has separate solutions, the two solutions can be written as \({(8y-11)^2}=169 \\ \downarrow Square-root \space both \space of \\ the \space equation \\ 8y-11=±13 \\ \downarrow Separate \space the \space solutions \\ 8y-11=13 \\ or \\ 8y-11=-13 \)
and this is why there are two answers.
