A movie theater sells popcorn and fountain drinks. Brett buys 1 popcorn bucket and 3 fountain drinks for his family, and pays $9.50. Sarah buys 3 popcorn buckets and 4 fountain drinks for her family, and pays a total of $19.75. If p represents the number of popcorn buckets and d represents the number of drinks.

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.