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:
| Outcome | Year | Championship | Surface | Opponent in the final | Score in the final |
| --- | --- | --- | --- | --- | --- |
| Runner-up | 1939.0 | French Championships | Clay | Don McNeill | 5–7, 0–6, 3–6 |
| Winner | 1939.0 | Wimbledon | Grass | Elwood Cooke | 2–6, 8–6, 3–6, 6–3, 6–2 |
| Winner | 1939.0 | US Championships | Grass | Welby Van Horn | 6–4, 6–2, 6–4 |
| Runner-up | 1940.0 | US Championships | Grass | Don McNeill | 6–4, 8–6, 3–6, 3–6, 5–7 |
| Winner | 1941.0 | US Championships | Grass | Frank Kovacs | 5–7, 6–1, 6–3, 6–3 |
Question:
How many years have an Opponent in the final of welby van horn?
Answer:
1939.0