user: ### NOW ANSWER:
Question: what is the platform when the frequency (per hour) is 4 and the destination is West Croydon?
Columns: ['Platform', 'Frequency (per hour)', 'Destination', 'Operator', 'Line']
Types: ['real', 'real', 'text', 'text', 'text']
Sample row: [1.0, 4.0, 'Highbury & Islington', 'London Overground', 'East London']
SQL:

assistant: SELECT SUM("Platform") FROM "Table" WHERE "Frequency (per hour)" = 4.0 AND "Destination" = 'West Croydon';