user: Question: Name the call sign for ERP W of 4
Columns: ['Call sign', 'Frequency MHz', 'City of license', 'ERP W', 'Class', 'FCC info']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['W212CA', '90.3 FM', 'Bay Minette, Alabama', 27.0, 'D', 'FCC']
SQL:

assistant: SELECT "Call sign" FROM "Table" WHERE "ERP W" = 4.0;