To pick the first team we have a choice of 9 for the first member, then 8 for the next and so on, the order doesn't matter so we need to take into account the 24 different ways of arranging 4 team members. That way we end up with combinations. So that's 9*8*7*6/24=126. We're now left with 5 people. There are 5 ways to pick 4 people out of 5, so the total number of ways of picking two different teams of four from nine people is 126*5=630.