Okay, in order to find this, you need to know how many variables are involved. In this case, there are 6 letters. So you multiply 6*5*4*3*2*1. Now if there was 10 letters, then you'd do 10*9*8 etc., etc. You get that? So do 6*5*4*3*2*1 and you get 720, so your answer here is C.