CREATE TABLE table_204_639 (id DECIMAL, "poll company" TEXT, "source" TEXT, "publication date" TEXT, "psuv" DECIMAL, "opposition" DECIMAL, "undecided" DECIMAL)

how many total opposition votes were cast after august 2010 ?
SELECT SUM("opposition") FROM table_204_639 WHERE "publication date" > (SELECT "publication date" FROM table_204_639 WHERE "publication date" = 'august 2010')
SELECT SUM("opposition") FROM "table_204_639" WHERE "publication date" > (SELECT "publication date" FROM "table_204_639" WHERE "publication date" = 'august 2010')