Answer
$15$
Work Step by Step
Use the formula $C(n,r)=\dfrac{n!}{r!(n-r)!}$ to obtain:
$C(6,2)=\dfrac{6!}{2!(6-2)!}$
$C(6,2)=\dfrac{6!}{2!(4!)}$
$C(6,2)=\dfrac{6{\times} 5 {\times} 4 {\times} 3 {\times} 2 {\times} 1}{(2 {\times} 1)(4{\times}3{\times}2{\times}1)}$
Simplify to get
$C(6,2)=15$
There are $15$ possible combinations.