CREATE TABLE table_21831 ("Year" FLOAT, "Network" TEXT, "Play-by-play" TEXT, "Colour commentator ( s ) " TEXT, "Sideline reporters" TEXT, "Pregame host" TEXT, "Pregame analysts" TEXT)

Who did the play-by-play when the pregame host was Brian Williams and the sideline reporters were Steve Armitage and Brenda Irving?
SELECT "Play-by-play" FROM table_21831 WHERE "Pregame host" = 'Brian Williams' AND "Sideline reporters" = 'Steve Armitage and Brenda Irving'
SELECT "Play-by-play" FROM "table_21831" WHERE "Pregame host" = 'Brian Williams' AND "Sideline reporters" = 'Steve Armitage and Brenda Irving'