From the diagram, we were told that
Triangle FGH is similar to triangle JKH. This means that
Angle F is congruent to anle J
Angle G is congruent to anle K
Angle GHF is congruent to angle KHJ
Since the triangles are similar, the ratio of the corresponding sides would be equal. Thus,
FG/JK = FH/JH = GH/KH