Answer
$35$
Work Step by Step
This involves combination (because order does not matter) in which $n=7$ and $r=4$.
Using the formula $C(n,r)=\dfrac{n!}{(n-r)!\times r!}$ gives:
$C(7,4)
\\=\dfrac{7!}{(7-4)!4!}
\\= \dfrac{7!}{3!\times4!}
\\= \dfrac{7\times6\times5\times4!}{3!\times4!}
\\= \dfrac{7\times6\times5}{3!}
\\=\dfrac{210}{6}
\\= 35$
