In δfgh point n is the midpoint of fr which segment is a median of δfgh a gr b fh c fn d gn

Choice D. Segment GN is a median

A median is a segment that goes from a triangle vertex to the midpoint of the opposite side. In this case, point G is the vertex and point N is the midpoint (of side FH). Check out the visual diagram attached below.

note: I'm assuming your teacher meant to say "midpoint of FH" instead of "midpoint of FR" because point R isn't mentioned at all in triangle FGH.

rounding to the nearest thousandth would be 452,000