Answer
$\left\{1, 2, 3, 4, 5, 6\right\}$
Work Step by Step
Recall:
The union of sets $A$ and $B$, denoted by $A \cup B$, contains the combined elements of the two sets .
Thus,
$A \cup B = \left\{1, 2, 3, 4, 5, 6\right\} \cup \left\{1, 3, 5\right\}=\left\{1, 2, 3, 4, 5, 6\right\}$
