The single tickmarks on YU and UV indicate they are the same length. These are the legs of the right triangles. We need info about each hypotenuse to be able to use HL. Specifically, if we knew that XY = VW, then we could use HL to prove the triangles congruent.
Fern's estimate is not correct because he rounded 548 wrong, it would be rounded to 550 instead since the number 8 is closer to 10. So the correct answer would be 420.
