CREATE TABLE table_name_73 (tonnage NUMBER, type_of_ship VARCHAR2, date_entered_service VARCHAR2)

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?
SELECT SUM(tonnage) FROM table_name_73 WHERE type_of_ship = "twin screw ro-ro motorship" AND date_entered_service = "11 february 1983"
SELECT SUM("tonnage") FROM "table_name_73" WHERE "11 february 1983" = "date_entered_service" AND "twin screw ro-ro motorship" = "type_of_ship"