Find the number of permutations of n different things taken r at a time such that the two specified things occur together?
Once you've those 2 things remaining things can be selected in C(n-2, r-2) ways. In each group arrangement can be done in (r-1)!.2! ways so that those 2 things are always together. Just multiply the above two. I've assumed that 2 specific things are always present in the permutation and are always together.