If a = {1, 2, 3} and b = {1, 2, 3, 4, 5, 6, 7, 8} then a ∪ b ø {1, 2, 3, 4, 5, 6, 7, 8} {1, 2, 3}

A is the set of values 1, 2, and 3 
B is the set of values 1, 2, 3, 4, 5, 6, 7, and 8

The notation A U B means "A union B". We simply throw all of the values from both sets into one bigger set. Toss out any duplicates as with set notation, only one unique value is allowed

Doing that leads to the answer {1, 2, 3, 4, 5, 6, 7, 8}

Side Note: All of the numbers in set A can be found in set B. So this means set A is a subset of set B. Therefore, A U B = B