Which Frequency has a Webcast of •, and a Callsign of xemr?
CREATE TABLE "long_range_am_stations" (
  "frequency" real,
  "callsign" text,
  "brand" text,
  "city_of_license" text,
  "website" text,
  "webcast" text
);
SELECT AVG("frequency") FROM "long_range_am_stations" WHERE "webcast"='•' AND "callsign"='xemr';