CREATE TABLE table_name_31 (frequency INT, webcast VARCHAR, callsign VARCHAR)

Which Frequency has a Webcast of , and a Callsign of xemr?
SELECT AVG(frequency) FROM table_name_31 WHERE webcast = "•" AND callsign = "xemr"
SELECT AVG("frequency") FROM "table_name_31" WHERE "callsign" = "xemr" AND "webcast" = "•"