user: Question: Which Men's 50 has a Senior Mixed of N/A, and a Men's Open of Gold Coast Sharks def Sydney Mets, and a Men's 30 of Sydney Mets def Sydney Scorpions, and a Women's u20 of Southern Suns def Brisbane City Cobras?
Columns: ['Year', "Men's Open", "Women's Open", 'Mixed Open', "Men's u20", "Women's u20", 'Senior Mixed', "Men's 30", "Women's 30", "Men's 35", "Women's 35", "Men's 40", "Women's 40", "Men's 45", "Men's 50"]
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1997.0, 'Sydney Scorpions def Brisbane City Cobras', 'Brisbane City Cobras def Sydney Mets', 'Sydney Rebels def Brisbane City Cobras', 'Brisbane City Cobras def Gold Coast Sharks', 'Sunwest Razorbacks def Sydney Rebels', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A', 'N/A']
SQL:

assistant: SELECT "Men's 50" FROM "Table" WHERE "Senior Mixed" = 'N/A' AND "Men's Open" = 'Gold Coast Sharks def Sydney Mets' AND "Men's 30" = 'Sydney Mets def Sydney Scorpions' AND "Women's u20" = 'Southern Suns def Brisbane City Cobras';