user: Question: What is the total erp w of class c3, which has a frequency mhz less than 89.9?
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("ERP W") FROM "Table" WHERE "Class" = 'c3' AND "Frequency MHz" < 89.9;