48*0.5+240+48X=72X
X= 1 1
That is, the express train needs 1 1 hour to catch up with the local train.
Because the express train is behind the local train, it has to walk at least 240 kilometers to catch the local train, so
Distance traveled by express train x hours = distance traveled by local train 30 minutes in advance+240km+distance traveled by local train x hours.
To tell the truth, this question is very simple.