What is the population of the Parish, Plumbland, that had a former local authority of Cockermouth Rural District?
CREATE TABLE "list_of_civil_parishes_and_unparished_ar" (
  "name" text,
  "status" text,
  "population" real,
  "district" text,
  "former_local_authority" text
);
SELECT COUNT("population") FROM "list_of_civil_parishes_and_unparished_ar" WHERE "former_local_authority"='cockermouth rural district' AND "name"='plumbland';