What is the fleet number when the transmission is Voith D863.4 and the engine is Cummins ISL?
CREATE TABLE "buses" (
  "fleet_num" text,
  "year" real,
  "manufacture" text,
  "model" text,
  "length_ft" real,
  "engine" text,
  "transmission" text
);
SELECT "fleet_num" FROM "buses" WHERE "transmission"='Voith D863.4' AND "engine"='Cummins ISL';