Schema: CREATE TABLE table_name_32 (platform INTEGER, destination VARCHAR, frequency__per_hour_ VARCHAR, operator VARCHAR)
Question: 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"