Question 19596
Initial distance between 2 trains=390 km
Final distance between 2 trains=0 km….(since they pass one another)
Hence distance traveled by both together=390-0=390 km
Let speed of express train =x kmph
30 kmph slower than above=x-30 kmph=speed of goods train
since both are traveling in opposite directions ,their relative speed is sum of their speeds =x+x-30=2x-30 kmph (note that with each passing hour,when the trains move in opposite directions,their distance of separation comes down by he sum of their speeds) 
time of travel =3 hrs. 
so we have…..relative speed =distance trvelled between final and initial stgs/time difference from beginning to end of travel
2x-30=390/3=130
2x=130+30=160
x=160/2=80
speed of express = 80 kmph
speed of goods = x-30 =80-30=50 kmph