user: ### NOW ANSWER:
Question: What year did Dave F. McTaggart win the men's singles and Robert B. Williams Ethel Marshall win the mixed doubles?
Columns: ['Year', "Men's singles", "Women's singles", "Men's doubles", "Women's doubles", 'Mixed doubles']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1957.0, 'Dave F. McTaggart', 'Judy Devlin', 'Don K. Smythe H. "Budd" Porter', 'Sue Devlin Judy Devlin', 'Robert B. Williams Ethel Marshall']
SQL:

assistant: SELECT MAX("Year") FROM "Table" WHERE "Men's singles" = 'Dave F. McTaggart' AND "Mixed doubles" = 'Robert B. Williams Ethel Marshall';