Use the Venn diagram below to answer the questions

1. U= {1, 2, 3, 4, 6, 9, 12, 18}
2. A= {1, 2, 3, 4, 6, 12}
3. B= {1, 2, 3, 6, 9, 18}
4. A∩B= {1, 2, 3, 6}
5. sign of a null set