Answer
See below
Work Step by Step
Find the midpoint of the line segment
$(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})=(\frac{4+10}{2},\frac{2+8}{2})=(7,5)$
Calculate the slope of AB:
$m=\frac{y_2-y_1}{x_2-x_1}=\frac{5-10}{7-3}=\frac{-5}{4}$
Use point-slope form:
$y-5=\frac{-5}{4}(x-7)\\y=-\frac{5}{4}x+\frac{55}{4}$