Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_40407 ( "Platform" real, "Frequency (per hour)" real, "Destination" text, "Service Pattern" text, "Operator" text, "Line" text )

### Question ###
How many frequencies have a line of East London and destination of Crystal Palace?

### Accurate SQL ###

SELECT COUNT("Frequency (per hour)") FROM table_40407 WHERE "Line" = 'east london' AND "Destination" = 'crystal palace'