Answer
$15$
Work Step by Step
The order doesn't matter here, thus we use combinations. We know that $C(n,r)=\frac{n(n-1)(n-2)...(n-k+1)}{r!}$. Also $C(n,0)=1$ by convention. Also $C(n,r)=C(n,n-r).$
Hence here $C(6,2)=\frac{6\cdot5}{2\cdot1}=15$.