@srestha we are considering group of 4 players, your first answer is valid if there would have been only 1 player. in b part we need to consider other combinations as well.
This can also be solved using multinomial coefficients
If there are n distinct objects to be placed in r groups having group size of n1,n2,.... then it can be done in
$\frac{n!}{n1!n2!n3!...nr!}$