Answer:
360
Step-by-step explanation:
Here we are required to find 
It is a problem of Permutation and we must understand the formula for finding permutations.
The general formula for finding the permutation is given as below:

Hence


Where



Hence





keep in mind, that "t" is the time when the train at A station, left towards B station
they met, at some time "t", and by the time that happened, train from A
which started 3 hours earlier, had already covered "d" distance,
whatever that is
and the train coming from B, covered, 600-d, or the difference
Ok, so remember the exponentioal law that says

so

answe ris x^6