user: Question: What is Winner, when Circuit is Mallala Motor Sport Park, and when Series is ASTC Round 6?
Columns: ['Date', 'Series', 'Circuit', 'City / State', 'Winner', 'Team']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['7 – 9 Mar', 'Super Touring GT-P Race', 'Albert Park', 'Melbourne , Victoria', 'Jim Richards', 'Volvo Cars Australia']
SQL:

assistant: SELECT "Winner" FROM "Table" WHERE "Circuit" = 'Mallala Motor Sport Park' AND "Series" = 'ASTC Round 6';