user: Question: What is the total number of discs where the run time was 4 hours 40 minutes?
Columns: ['DVD Name', 'Released', 'Audio', 'Aspect Ratio', 'Duration', 'Number of Episodes', 'Num of Discs']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'real']
Sample row: ['Escape To River Cottage', '08/09/2003', 'Dolby Digital 2.0', '4:3 Full Frame', '2 hours 48 minutes', 6.0, 2.0]
SQL:

assistant: SELECT SUM("Num of Discs") FROM "Table" WHERE "Duration" = '4 hours 40 minutes';