[填空题]
An earthquake P wave tbyk no4a +a69*d+ugi traveli4c6eh9a;ey r l rx/l8(y* jim( jmar9dng at k.0 km/s strikes a boundary within the Earth between two kinds of material. If it approaches the ;arlmdy4m 9h9eyj8r6 r(xl( je /a* icboundary at an incident angle of 47 $^{\circ} $ and the angle of refraction is 35 $^{\circ} $, what is the speed in the second medium? km/s
