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