Harper is ordering a sandwich from a deli. There are 9 types of meat to choose from and 7 cheeses, and Harper must pick one of each. How many different sandwiches can Harper
order?
___sandwiches

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.