Say that the front four people's names are John, Kathy, Mia, and Alex, in that order. You can arrange them as follows.
John, Kathy, Alex, Mia John, Alex, Kathy, Mia John, Alex, Mia, Kathy John, Mia, Alex, Kathy John, Mia, Kathy, Alex Alex, John, Kathy, Mia Alex, John, Mia, Kathy There are many more, but my guess would be 16 combinations. Test for yourself if you don't think thats right!
The first chair can be any one of the 15. For each of those ... The second chair can be any one of the remaining 14. For each of those ... The third chair can be any one of the remaining 13. For each of those ... The fourth chair can be any one of the remaining 12.
Number of ways to fill the 4 chairs = (15 x 14 x 13 x 12) = 32,760 .
But ...
Each set of 4 people can be seated in (4 x 3 x 2 x 1) = 24 orders. So each group of 4 people is represented 24 times among the 32,760.
If the order doesn't matter, you're really asking how many different groups of 4 people can occupy the front row.
That's (32,760) / (24) = 1,365 sets of 4 members, in any order.
Usually AND refers to adding, that's just the rules of math according to writing equation. Times would be multiplying, taking away is subtraction and divided by is dividing.