PLS HELP

use $(\frac{x_{1}+x_{2}}{2}, \frac{y_{1}+y_{2}}{2})$

for $(3+\sqrt{2},5)$ and $(4, 7)$ :

$( \frac{3+\sqrt{2}+4}{2}, \frac{5+7}{2})$

$D_{s1}=( 4.2, 6)$

for the 2nd one $(6-\sqrt{2},3)$ and $(3, \: 5)$

$( \frac{6-\sqrt{2}+3}{2}, \frac{3+5}{2} )$

$D_{s2}=(3.8,\: 4 )$

so the coordinates of the midline are $( 4.2, 6)$ and $(3.8,\: 4 )$

again doing the same thing:

$( \frac{4.2+3.8}{2}, \frac{6+4}{2} )$

$\boxed{D_{s3(midline)}=(4,\: 5) }$