If a = {x | x is an even integer}, b = {5, 6, 7, 8}, list the elements of the set a u b

First of all, what is an integer?

Integers are numbers such as -7, -4, 0, 5, 16... etc...

This means that even integers are numbers such as:

-4, -2, 0, 2, 4, 6, 8, 10... etc...

Which means that:

AUB={..., -4, -2, 0, 2, 4, 5, 6, 7, 8, 10, 12, 14, ...}

This is because:

The union "U" of two sets must contain all the numbers from both sets, providing they aren't duplicated.