Answer
$28$
Work Step by Step
Since $\left(\begin{array}{c} n\\ r\end{array} \right)=\dfrac{n!}{r!(n-r)!}$, then, $\left(\begin{array}{c}
8 \\ 2
\end{array} \right)$ is equal to
\begin{array}{l}\require{cancel}
\dfrac{8!}{2!(8-2)!}
\\\\=
\dfrac{8!}{2!(6)!}
\\\\=
28
\end{array}