How many house mascots are associated with yellow house colours?
CREATE TABLE "whanau_house_system" (
  "house_name" text,
  "house_mascot" text,
  "house_colour" text,
  "year_opened" real,
  "house_leader" text
);
SELECT COUNT("house_mascot") FROM "whanau_house_system" WHERE "house_colour"='Yellow';