what is the highest platform number one when frequency ( hours) 4, operator london overground and destination west croydon?
Platform Frequency (per hour) Destination Operator Line
Honor Oak Park railway station
1132489
real real text text text
2-1132489-1
Services
Services
1 4 Highbury & Islington London Overground East London
1 4 Dalston Junction London Overground East London
1 4 London Bridge Southern Metro
2 4 Crystal Palace London Overground East London
2 4 West Croydon London Overground East London
2 2 London Victoria (Mon-Sat) Southern Metro
2 2 Caterham (Mon-Sat) Southern Metro
2 2 West Croydon (Peaks & Sun only) Southern Metro
2 2 Tattenham Corner (Sun only) Southern Metro
SELECT MAX Platform FROM table WHERE Frequency (per hour) = 4 AND Operator = london overground AND Destination = west croydon
4 london overground west croydon