Answer :
[tex]\begin{gathered} \Rightarrow(4,8)=(\frac{9+x}{2},\frac{-10+y}{2}) \\ \Rightarrow4=\frac{9+x}{2}\Rightarrow x=-1 \\ \Rightarrow8=\frac{-10+y}{2}\Rightarrow y=26 \\ \text{The other endpoint is (-1,26)} \end{gathered}[/tex]