Table: radio_stations_21
Columns: call_sign
frequency_mhz
city_of_license
erp_w
class
fcc_info

Question: What is the call sign for a class of A?
SQL: SELECT "call_sign" FROM radio_stations_21 WHERE "class" = 'a'

Question: What is the average frequency MHz for license of eastville, virginia?
SQL: SELECT AVG("frequency_mhz") FROM radio_stations_21 WHERE "city_of_license" = 'eastville, virginia'

Question: What is the average ERP W when the call sign is whre?
SQL: SELECT AVG("erp_w") FROM radio_stations_21 WHERE "call_sign" = 'whre'