Algebra 1: Common Core (15th Edition)

$A ∪ C$ = {1, 2, 3, 4, 5, 7, 10}
In unions, we must include all elements in the sets that are specified. Therefore, we will list all the elements of both $A$ and $C$: $A ∪ C$ = {1, 2, 3, 4, 5, 7, 10}