Answer
$_{30}C_4=27,405$
Work Step by Step
RECALL:
$_nC_r = \dfrac{n!}{r!(n-r)!}$
Use this definition to have:
$\require{cancel}
_{30}C_4=\dfrac{30!}{4!(30-4)!}
\\_{30}C_4=\dfrac{30!}{4!(26!)}
\\_{30}C_4 = \dfrac{30(29)(28)(27)(26!)}{24(26!)}
\\_{30}C_4 = \dfrac{30(29)(28)(27))\cancel{(26!)}}{24\cancel{26!}}
\\_{30}C_4 =\dfrac{30(29)\cancel{(28)}7(27)}{\cancel{24}6}
\\_{30}C_4 =\dfrac{5\cancel{30}(29)(7)(27)}{\cancel{6}}
\\_{30}C_4=27,405$
