Name the sum of ERP W for class of d and frequency mhz of 98.7
CREATE TABLE "translators" (
  "call_sign" text,
  "frequency_m_hz" real,
  "city_of_license" text,
  "erp_w" real,
  "class" text,
  "fcc_info" text
);
SELECT SUM("erp_w") FROM "translators" WHERE "class"='d' AND "frequency_m_hz"=98.7;