A train that is \(400\) metres long approaches a tunnel that is \(1200\) metres long. The entire train is completely in the tunnel for \(30\) seconds. That is, from the time that the last car on the train has completely entered the tunnel until the time when the front of the train emerges from the other end of the tunnel, \(30\) seconds pass. If the train is travelling at a constant speed, determine this speed in kilometres per hour.
Themes: Geometry & Measurement, Number Sense