Question 485928
before second train leaves station M 
first train is already 35 km ahead.

Because in 1 hour it travels 35 km.

catchup distance = 35

catchup speed = 40 -35 = 5 km/h

t= distance /speed
t = 35/5
t = 7 hours
it takes 7 hours for second train to catch up.
In 7 hours it travels 7 * 48 = 280 km