You can put this solution on YOUR website! If your calculator has a ! button, it's usually under the probability section.
If you just have a four function calculator then n! = n*(n-1)*(n-2)...*1
So, we can evaluate 12! as:
12*11*10*9*8*7*6*5*4*3*2*1
and 8! = 8*7*6*5*4*3*2*1
Then you see that we can cancel out 8*7*6*5*4*3*2*1 to get
12*11*10*9 = 11880