i know that already but how do i complete the problem?
If you knew all that already it would have been good for you to have said so in the OP so that people didn't end up wasting their time explaining it. And it wouldn't have hurt to Thank those people for their effort.
To complete the problem you substitute the fact that 8! = 8x7x6x5!, cancel the common factor of 5! and then do some basic arithmetic.