Two one-way subway lines, the A train line and the B train line, intersect at a transfer station.

Two one-way subway lines, the A train line and the B train line, intersect at a transfer station. A trains and B trains arrive at the station according to independently operating Poisson processes lambda_a=3 A trains per hour and lambda_B=6 B trains per hour

1) Whenever an A train is ready to depart from the station, it will be held if an approaching B train is within 30 seconds of the station. This delay policy is to facilitate the rapid transfer of passengers from the B train to the A train.

i.