What I know 
Train is 1km long 
Tunnel is 3km long 
Car goes in and comes out in 30 seconds 
Q: how fast does the train goes in km per hour

3000-1000=2000
2000
-------- = 66.7 in 1 second the train travels 66.7 metres
30
66.7 multiply by 60 =4000.2 That means every 1 minute it 
Travels 4000.2 meters every minute 

4000.2 multiply by 60=240012 every hour it travels that many metres

240012 divide by 1000= 240.012km per hour 

The train travels 240.012 km per hours