And ! (asap)
a freight train left seoul and traveled north at an average speed of 15.6 km/h. a passenger train left 3.9 hours later and traveled in the same direction but with an average speed of 39 km/h. how long did the freight train travel before the passenger train caught up?
( and explain)

Let's look at the difference in speed between the two: it's 39-15.6=23.4 km/h

(we can just subtract this because they are traveling in the same direction) - this means that it's as if the slower train (the freight) was in place and the passenger train was traveling at 23.4 km/h
No, the freighter left 3.9 hours earlier, during which it traveled

15.6*3.9=60.84 km

So they will meet when the passenger train will catch up on those 60.84 km.

It does it with 23.4 km/h so it will need:


So the freighter will be travellinf for 2.6 more hours than the other train - a total of (2.6+3.9=6.5) 6.5 hours!