how many times is the fuel propulsion is cng?
CREATE TABLE "fleet" (
  "order_year" text,
  "manufacturer" text,
  "model" text,
  "fleet_series_quantity" text,
  "powertrain_engine_transmission" text,
  "fuel_propulsion" text
);
SELECT COUNT("fleet_series_quantity") FROM "fleet" WHERE "fuel_propulsion"='CNG';