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:
| Date | Ship Name | Flag | Tonnage ( GRT ) | Fate | Deaths |
| --- | --- | --- | --- | --- | --- |
| 26 September 1940 | Ashantian | Great Britain | 4917.0 | Damaged | 4.0 |
| 26 September 1940 | Manchester Brigade | Great Britain | 6042.0 | Sunk | 56.0 |
| 26 September 1940 | Stratford | Great Britain | 4753.0 | Sunk | 2.0 |
| 14 October 1940 | HMS Cheshire * | Great Britain | 10552.0 | Damaged | 0.0 |
| 13 November 1940 | Cape St. Andrew | Great Britain | 5094.0 | Sunk | 15.0 |
| 16 November 1940 | Planter | Great Britain | 5887.0 | Sunk | 13.0 |
| 17 November 1940 | Saint Germain | Great Britain | 1044.0 | Sunk | 0.0 |
| 17 November 1940 | Veronica | Sweden | 1316.0 | Sunk | 17.0 |
Question:
Which tonnage has a Date of 26 september 1940, and a Ship Name of ashantian?
Answer:
4917.0