數學問題 Math Problem ?

在某校制足球賽中，每隊由1守門員及6名其他球員所組成。若校隊的教練從15名男孩中挑選球員，而當中有3位是守門員，
In a school-based football game, each team consists of 1 goalkeeper and 6 other players. If the coach of the school team selects players from 15 boys and 3 of them are goalkeepers,a) 求組成校隊共有多少種不同的結果。Find how many different results there are to form a school teamb) 若從餘下的球員，不理會職責安排替補的次序，有多少種選擇。
From the remaining players, regardless of the order of responsibilities, how many choices are there