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:
| Gauge | Railway | Class | Works no. | Year | Builder |
| --- | --- | --- | --- | --- | --- |
| 3 ft 6 in | Rhodesia Railways | 15th | 6936–6939 | 1940 | Beyer, Peacock |
| 3 ft 6 in | Rhodesia Railways | 15th | 7228–7237 | 1947 | Beyer, Peacock |
| 3 ft 6 in | Rhodesia Railways | 15th | 7260–7279 | 1948–49 | Beyer, Peacock |
| 3 ft 6 in | Rhodesia Railways | 15A | 7326–7340 | 1949–50 | Beyer, Peacock |
| 3 ft 6 in | Rhodesia Railways | 15A | 7351–7365 | 1950 | Beyer, Peacock |
| 3 ft 6 in | Rhodesia Railways | 15A | 2963–2972 | 1952 | Franco-Belge , France |
| 3 ft 6 in | Sudan Railways | 250 | 6798–6801 | 1936 | Beyer, Peacock |
| 3 ft 6 in | Sudan Railways | 250 | 6870–6875 | 1937 | Beyer, Peacock |
Question:
Which works number has a class of 15th and year of 1940?
Answer:
6936–6939