7c2 is how many different combinations of 2 you can make out of 7 choices

For EACH of those combinations the second team can make 7c2 choices

and for EACH of THOSE choices the THIRD team can make 7c2 choices

and for EACH of THOSE choices, the FOURTH team can make 7 c 3 choices

7c2 = 21 7c3 = 35

THEN there are FOUR ways to pick the host team , multiply THAT by 4:

7c2 x 7c2 x 7c2 x 7c3 x 4