For any given set in a tennis tournament, opponent A can beat opponent B in seven different

Question:

For any given set in a tennis tournament, opponent A can beat opponent B in seven different ways. (At 6-6 they play a tie breaker.) The first opponent to win three sets wins the tournament.
(a) In how many ways can scores be recorded with A winning in five sets?
(b) In how many ways can scores be recorded with the tournament requiring at least four sets?