What is the average ERP W when the call sign is whre?
CREATE TABLE "repeaters" (
  "call_sign" text,
  "frequency_m_hz" real,
  "city_of_license" text,
  "erp_w" real,
  "class" text,
  "fcc_info" text
);
SELECT AVG("erp_w") FROM "repeaters" WHERE "call_sign"='whre';