What is the average drop zone time in the N drop zone for the 1st Pathfinder Prov.?
CREATE TABLE "air_movement_table_mission_boston" (
  "serial" real,
  "airborne_unit" text,
  "troop_carrier_group" text,
  "num_of_c_47s" real,
  "uk_base" text,
  "drop_zone" text,
  "drop_zone_time" real
);
SELECT AVG("drop_zone_time") FROM "air_movement_table_mission_boston" WHERE "drop_zone"='n' AND "troop_carrier_group"='1st pathfinder prov.';