user: Question: What's the sum of Quantity for the Class of 1928 of Ci-30?
Columns: ['Class to 1928', 'Class from 1928', 'Seats', 'Quantity', 'Year(s) of Manufacture']
Types: ['text', 'text', 'text', 'real', 'text']
Sample row: ['Di-26', 'Cid-26', '66', 77.0, '1927/28']
SQL:

assistant: SELECT SUM("Quantity") FROM "Table" WHERE "Class from 1928" = 'Ci-30';