The guards of two goods trains are in the respective last carriages of their trains. The two trains A and B of length 200 m and 300 m respectively, begin to enter a 500-metre long tunnel from opposite ends. The guard of one of the trains wants to pick up a flag from the other guard. How long after the instant when the two trains begin to enter the tunnel, does this exchange occur? (Given that speed of train A = 2 m/s, speed of train B = 3 m/s)

1) 180 sec
2) 225sec
3) 220 sec
4) 200 sec