user: Question: Name the sum of ERP W for class of d and frequency mhz of 98.7
Columns: ['Call sign', 'Frequency MHz', 'City of license', 'ERP W', 'Class', 'FCC info']
Types: ['text', 'real', 'text', 'real', 'text', 'text']
Sample row: ['WZAE', 93.3, 'Wadley, Georgia', 4000.0, 'A', 'FCC']
SQL:

assistant: SELECT SUM("ERP W") FROM "Table" WHERE "Class" = 'd' AND "Frequency MHz" = 98.7;