A is the set of values 1, 2, and 3
B is the set of values 1, 2, 3, 4, 5, and 6
Basically notation A U B means this "A union B". So we just combine all of the values from both A and B into one giant set. Then we reamove all of the duplicates as with set notation, and only one unique value is allowed
Doing that leads to the answer {1, 2, 3, 4, 5, 6}
Plus since the numbers in set A also can be found in set B means that set A is a subset of set B. A U B = B
