Answer
203490.
Work Step by Step
$_{n}C_{r}=\frac{n!}{(n-r)!r!}$
$_{21}C_{8}=\frac{21!}{(21-8)!8!}=\frac{21\times20\times19\times18\times17\times16\times15\times14\times13!}{13!\times8!}=\frac{21\times20\times19\times18\times17\times16\times15\times14}{8\times7\times6\times5\times4\times3\times2\times1}=203490$
