Bisector passes through midpoint
Midpoint of (7,1) and (3,5)
Perpendicular bisector has slope that is negative reciprocal of line segment joining points (7,1)and (3,5)
Slope of line segment
Perpendicular bisector has slope = 1 and passes through point (4,4)
Use point slope form
y-3=1(x-5)
y=x-2