Not sure how many questions there are, but here goes with 6 and 7.
Let's imagine there are 28 games. Team A wins 7 games and Team B wins 12 games. That means Team A has a probability of winning 7/28=1/4 and Team B a probability of winning 12/28=3/7. So when we look at all 28 games, we know that 19 games are won by either Team A or B. So the probability of either team winning must be 19/28.
Answer to 7 in comment...