CREATE TABLE "services" (
  "platform" real,
  "frequency_per_hour" real,
  "destination" text,
  "operator" text,
  "line" text
);

Question: what is the platform when the frequency (per hour) is 4 and the destination is west croydon?
SQL: SELECT SUM("platform") FROM "services" WHERE "frequency_per_hour"=4 AND "destination"='west croydon';

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 "services" WHERE "frequency_per_hour"=4 AND "operator"='london overground' AND "destination"='west croydon';