If $A$ is the set of factors of $35$ and $B$ is the set of factors of $45$, then $A \cap B =$

The factors of $35$ are $\{1, 5, 7, 35\}$ and the factors of $45$ are $\{1, 3, 5, 9, 15, 45\}$. The only common factors are and , so .