I don't understand disjoint sets. Can someone please explain how this answer was obtained?

Let the array form of the disjoint sets be as follows. A | -4 | 1 | 1 | 3 | 3 | 5 | 5 | -3 | 8 | 8 | 10 | 10 | 12 | 12 | i | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | | 9 | 10 | 11 | 12 | 13 | 14 | Assume that we are using union by rank and find with path compression. Show the array form of the resulting disjoint sets after the operation union(6, 13). Solution: After the operation union(6, 13), the array form is as follows A | -4 | 1 | 1 | 3 | 1 | 1 | 5 | 1 | 8 | 8 | 10 | 8 | 8 | 12 | i | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | Grading Keys: 2 pts for correct root; 2 pts for correct rank of root; 2 pts for the path compression associated with each find