user: ### NOW ANSWER:
Question: What is the frequency MHz of the ERP W's greater than 250?
Columns: ['Call sign', 'Frequency MHz', 'City of license', 'ERP W', 'Class', 'FCC info']
Types: ['text', 'real', 'text', 'real', 'text', 'text']
Sample row: ['K208CL', 89.5, 'Tribune, Kansas', 250.0, 'D', 'FCC']
SQL:

assistant: SELECT AVG("Frequency MHz") FROM "Table" WHERE "ERP W" > 250.0;