class Vehicle:
    def __init__(self,speed):
        self.speed=speed

    def drive(self,distance):
        print 'need %f hour(s)' % (distance/self.speed)

class Bike(Vehicle):
    pass

class Car(Vehicle):
    def __init__(self,speed,fuel):
        Vehicle.__init__(self,speed)
        self.fuel=fuel

    def drive(self,distance):
        Vehicle.drive(self,distance)
        print 'need %f fuel' %(distance*self.fuel)

b=Bike(15.0)

c=Car(80.0,0.012)

b.drive(100)

c.drive(100)
