Answer: Hello mate!
first, let's do a list with all the things we know about this problem:
Both trains depart at the same time; we can define this time as t = 0 in hours.
the velocity of train A is 50mph
the velocity of train B is 60mph
both trains travel in opposite directions.
the initial distance between both trains is equal to 330 miles:
we want to know when the trains will meet each other:
The trains will meet each other when the sum of their traveled distance is equal to the initial separation between them.
the distance traveled by the train A is equal to his velocity multiplied by the time that passed since it departed.
this is: Da(t) = (50*t)mi
and the distance for the train B is: Db(t) = (60*t)mi
then, as we know, the trains will meet when Da(t) + Db(t) = 330mi
then 50*t + 60*t = 330
110*t = 330
t = 330/110 = 3h
the trains will meet 3 hours after they departed.