user: Question: What frequency has call sign W228BG?
Columns: ['Call sign', 'Frequency MHz', 'City of license', 'ERP W', 'Class', 'FCC info']
Types: ['text', 'real', 'text', 'real', 'text', 'text']
Sample row: ['W261CQ', 100.1, 'Decatur, Illinois', 99.0, 'D', 'FCC']
SQL:

assistant: SELECT "Frequency MHz" FROM "Table" WHERE "Call sign" = 'W228BG';