Because A has won two games at this time, and B has only won one game, so at most one side will win after two games.

Then, if A wins the fourth game, A will eventually get the 400 yuan (probability is 1/2).

If B wins the fourth game and A wins the fifth game, then A wins the 400 yuan (probability is 1/4).

If B wins the fourth game and B wins the fifth game, then B wins the 400 yuan (probability is 1/4).

Therefore, the probability that A finally gets the 400 yuan is 1/2+ 1/4=3/4.

B The probability of finally getting this 400 yuan is 1/4.

So A should get 400*3/4=300.

B should get 400* 1/4= 100.