8Pn=8×7×6=8P3 so n=3, the number of permutations of 3 items out of 8.
Here's how it works:
If we have 8 items and we wish to select 3, one by one, then we have a choice of any one of 8 for the first selection, leaving 7 to choose from next; so we have 8×7=56 possible permutations (each of the 8 first choices combines with each of the 7 second choices). There are now 6 items left, so we have 8×7×6=336 possible permutations in selecting 3 items out of 8. (In permutations the order is important. In combinations, the order is irrelevant. Selecting A then B then C in that order is not the same permutation as selecting C then A then B. But it is the same combination. The number of combinations is always less than the number of permutations.)