midpoint of (x1,y1) and (x2,y2) is
[tex](\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})[/tex]
so the midpoint of HX is the mdpoint of (13,8) and (-6,-6)
which is
[tex](\frac{13-6}{2},\frac{8-6}{2}=[/tex]
[tex](\frac{7}{2},\frac{2}{2}=[/tex]
[tex](3.5,1)[/tex]
the midpoint is (3.5,1)
