I thought I had this question solved and I sort of did bu I got only half of the answer.

Solve ....

6Pn=720

so what I did was

6!/(6-n)!=720

6!/720=(6-n)! ****Also why cant you cancel the ! here, I mean why cant you divide it out here?

6x5x4x3x2x1/720=6-n

720/720=6-n

n=6-1

n=5

but the answer that is given is 5 or 6? where is this 6 coming from?