user: Question: What is the total frequency mhz of the kgrj call sign, which has an erp w greater than 21500?
Columns: ['Call sign', 'Frequency MHz', 'City of license', 'ERP W', 'Class', 'FCC info']
Types: ['text', 'real', 'text', 'real', 'text', 'text']
Sample row: ['KGKD', 90.5, 'Columbus, Nebraska', 10000.0, 'C2', 'FCC']
SQL:

assistant: SELECT SUM("Frequency MHz") FROM "Table" WHERE "Call sign" = 'kgrj' AND "ERP W" > 21500.0;