What is the average pjehun measured by female enrollment?
CREATE TABLE "primary_education_statistics_by_district" (
  "measure" text,
  "bombali" real,
  "bonthe" real,
  "kailahun" real,
  "kambia" text,
  "kenema" real,
  "koinadugu" real,
  "kono" real,
  "moyamba" text,
  "port_loko" text,
  "pujehun" real,
  "tonkolili" real
);
SELECT AVG("pujehun") FROM "primary_education_statistics_by_district" WHERE "measure"='female enrollment';