Tyne and Wear County has what total membership for their metropolitan area?
CREATE TABLE "group_membership" (
  "city" text,
  "county" text,
  "region" text,
  "local_authority" text,
  "type" text,
  "population" real,
  "urban_area" real,
  "metropolitan_area" real
);
SELECT "metropolitan_area" FROM "group_membership" WHERE "county"='Tyne and Wear';