A group of k elements can be chosen from a group of n elements in [tex]\frac{n!}{k!(n-k)!}[/tex] ways.
[tex](^6 _4)=\frac{6!}{4!(6-4)!}=\frac{6!}{4! \times 2!}=\frac{4! \times 5 \times 6}{4! \times 2}=\frac{5 \times 6}{2}=5 \times 3=15[/tex]
A group of 4 people can be selected from a group of 6 people in 15 ways.
