CREATE TABLE table_6555 ("Task No." FLOAT, "Day announced" TEXT, "Options" TEXT, "Viewers' selection" TEXT, "Result" TEXT)

when was it announced that the viewers selected robi out of alex, ejay, nan, robi?
SELECT "Day announced" FROM table_6555 WHERE "Viewers' selection" = 'robi' AND "Options" = 'alex, ejay, nan, robi'
SELECT "Day announced" FROM "table_6555" WHERE "Options" = 'alex, ejay, nan, robi' AND "Viewers' selection" = 'robi'