What is the WPW freq with a day power of 250?
CREATE TABLE "am" (
  "freq" real,
  "call" text,
  "city" text,
  "owner" text,
  "day_power_w" real,
  "night_power" real,
  "format" text,
  "stereo" text
);
SELECT SUM("freq") FROM "am" WHERE "owner"='wpw' AND "day_power_w">250;