What is the authority status of the school in Ellerslie with a decile of 7?
CREATE TABLE "maungakiekie_tamaki_local_board" (
  "name" text,
  "years" text,
  "area" text,
  "authority" text,
  "decile" text,
  "roll" real
);
SELECT "authority" FROM "maungakiekie_tamaki_local_board" WHERE "area"='ellerslie' AND "decile"='7';