There are many possible numbers. First, lets begin with the data there giving us. They are saying she wants to play a practice game so there at least needs to be 2 teams. It also says, that she wants 6 players on each team, nothing more and nothing less. So, for this we are going to use the 6 timetables.
6 x 2 = 12
6 x 3 = 18
6 x 4 = 24
6 x 5 = 30
6 x 6 = 36
There are also more numbers, but I am not doing those. But, for your first five, there can be 12, 18, 24, 30, and 36 students to be on the teams for the practice game.