CREATE TABLE table_name_21 (class VARCHAR, frequency_mhz VARCHAR, call_sign VARCHAR)

Which Class has a Frequency MHz larger than 91.7, and a Call sign of k272ec?
SELECT class FROM table_name_21 WHERE frequency_mhz > 91.7 AND call_sign = "k272ec"
SELECT "class" FROM "table_name_21" WHERE "call_sign" = "k272ec" AND "frequency_mhz" > 91.7