CREATE TABLE table_name_32 (platform INTEGER, destination VARCHAR(255), frequency__per_hour_ VARCHAR(255), operator VARCHAR(255))
what is the highest platform number when the frequency (per hour) is 4, the operator is london overground and the destination is west croydon?
    
SQL: SELECT MAX(platform) FROM table_name_32 WHERE frequency__per_hour_ = 4 AND operator = "london overground" AND destination = "west croydon"