The midpoint is (3,20) and the other endpoint is (10,13);
Since the midpoint formula is;
[tex](x_m,y_m)=(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})[/tex]Thus;
[tex]\begin{gathered} x_m=\frac{x_1+x_2}{2} \\ 3=\frac{x_1+10}{2} \\ x_1+10=6 \\ x_1=-4 \end{gathered}[/tex]and;
[tex]\begin{gathered} y_m=\frac{y_1+y_2}{2} \\ 20=\frac{y_1+13}{2} \\ y_1+13=40 \\ y_1=27 \end{gathered}[/tex]Thus, the other endpoint is;
[tex](-4,27)[/tex]