Answer
$_9P_4=3, 024$
Work Step by Step
RECALL:
$_nP_r = \dfrac{n!}{(n-r)!}$
Use this definition to have:
$\require{cancel}
_9P_4=\dfrac{9!}{(9-4)!}
\\_9P_4=\dfrac{9!}{5!}
\\_9P_4 = \dfrac{9(8)(7)(6)(5!)}{5!}
\\_9P_4 = \dfrac{9(8)(7)(6)\cancel{(5!)}}{\cancel{5!}}
\\_9P_4=3, 024$