How many rafters are needed for a home with a gable roof that measures 48′ by 34′? the rafters are spaced 18″ o.c. and the roof has a 3′ overhang

How many rafters are needed for a home with a gable roof that measures 48′ by 34′? the rafters are spaced 18″ o.c. and the roof has a 3′ overhang