user: Question: what is the sum of tonnage when the type of ship is Twin Screw Ro-Ro Motorship and the date entered service is 11 February 1983?
Columns: ["Ship's name", 'Date entered service', 'Date withdrawn', 'Tonnage', 'Type of Ship']
Types: ['text', 'text', 'text', 'real', 'text']
Sample row: ['Oranje Nassau', '27 August 1945', 'July 1954', 3053.0, 'Twin Screw Steamer']
SQL:

assistant: SELECT SUM("Tonnage") FROM "Table" WHERE "Type of Ship" = 'Twin Screw Ro-Ro Motorship' AND "Date entered service" = '11 February 1983';