Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Source | Date | Goldberg | Murray | Silbert | Undecided |
| --- | --- | --- | --- | --- | --- |
| Suffolk University | September 15–17, 2006 | 35% | 22% | 21% | 31% |
| Boston Globe | September 12–15, 2006 | 26% | 20% | 18% | 27% |
| State House News | September 7–10, 2006 | 18.3% | 15.2% | 10.0% | 53.4% |
| Suffolk University | August 19–21, 2006 | 6% | 11% | 5% | 77% |
| Suffolk University | June 22–26, 2006 | 10% | 6% | 5% | 79% |
Question:
What is the date of the poll with Silbert at 18%?
Answer:
September 12–15, 2006