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:
| State | Type | Name | Title | Royal house | From | To |
| --- | --- | --- | --- | --- | --- | --- |
| Chu | Sovereign | Huai | King | Mi | 328 BC | 299 BC |
| Han | Sovereign | Xiang | Marquis | — | 311 BC | 296 BC |
| Lu | Sovereign | Wen II | Duke | Ji | 302 BC | 280 BC |
| Qi | Sovereign | Min | King | Tian | 300 BC | 284 BC |
| Qin | Sovereign | Zhaoxiang | King | Ying | 306 BC | 251 BC |
| Song | Sovereign | Kang | King | — | 328 BC | 286 BC |
| Wei | Sovereign | Xiang | King | — | 318 BC | 296 BC |
| Wey | Sovereign | Si Jun | Marquis | — | 334 BC | 293 BC |
| Yan | Sovereign | Zhao | King | — | 311 BC | 279 BC |
| Zhao | Sovereign | Wuling | King | — | 325 BC | 299 BC |
Question:
what is the total number of known vassal states in which their reigning years are known?
Answer:
10