Question 894464
The train is 0.5 km in length.  When front of the train is at the threshold of the tunnel entrance, the REAR of the train has 0.5+4.5 km of travel to reach the other end of the tunnel.


All parts of the train are moving at  50 km/hour.
RT=D for uniform travel rates.
T=D/R
Here, {{{highlight(T=(0.5+4.5)/50)}}}  HOURS, which you might want to convert to minutes.