CREATE TABLE table_11900773_6 (first_day_cover_cancellation VARCHAR, date_of_issue VARCHAR, theme VARCHAR)

Where is the first day cover cancellation for the 3 April 2008 IIHF World Championships, Quebec City stamp?
SELECT first_day_cover_cancellation FROM table_11900773_6 WHERE date_of_issue = "3 April 2008" AND theme = "IIHF World Championships, Quebec City"
SELECT "first_day_cover_cancellation" FROM "table_11900773_6" WHERE "3 April 2008" = "date_of_issue" AND "IIHF World Championships, Quebec City" = "theme"