user: Question: How many frequencies have a line of east london and destination of crystal palace?
Columns: ['Platform', 'Frequency (per hour)', 'Destination', 'Service Pattern', 'Operator', 'Line']
Types: ['real', 'real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 4.0, 'Highbury & Islington', 'All stations via Shoreditch High Street', 'London Overground', 'East London']
SQL:

assistant: SELECT COUNT("Frequency (per hour)") FROM "Table" WHERE "Line" = 'east london' AND "Destination" = 'crystal palace';