user: Question: What is the frequency of the radio station with a call sign of WGNR-FM?
Columns: ['Call sign', 'Frequency', 'City of license', 'State', 'FCC info']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['WMBV', '91.9 FM', 'Dixons Mills', 'Alabama', 'FCC']
SQL:

assistant: SELECT "Frequency" FROM "Table" WHERE "Call sign" = 'WGNR-FM';