39. The little trains on多多Island are busily working. Thomas and Percy travel from the shed to the harbor, while Edward travels from the harbor to the station. They all immediately return to their starting points after reaching their destinations, completing one round trip before finishing their work. The three trains start at the same time. When Edward arrives at the station, Thomas also happens to be passing the station, while Percy has only traveled $45 \mathrm{~km}$; when Edward returns to the harbor, Thomas is passing the station again. At this point, Thomas's steam engine malfunctions, and he continues at half speed, meeting Percy face-to-face at the midpoint of the line between the shed and the harbor. What is the length of the railway line between the shed and the harbor in $\mathrm{km}$?
$225$