CREATE TABLE table_15845 ("Order Year" TEXT, "Manufacturer" TEXT, "Model" TEXT, "Fleet Series  ( Quantity ) " TEXT, "Powertrain  ( Engine/Transmission ) " TEXT, "Fuel Propulsion" TEXT)

how many times is the fuel propulsion is cng?
SELECT COUNT("Fleet Series (Quantity)") FROM table_15845 WHERE "Fuel Propulsion" = 'CNG'
SELECT COUNT("Fleet Series (Quantity)") FROM "table_15845" WHERE "Fuel Propulsion" = 'CNG'