a girl wants to take some cakes to her grandmother for her birthday but granny lives up the valley and the girl has to pass over 7 bridges to get to grandmas
each bridge has a toll to be paid ,the toll is half of the girls cakes but the toll masters being a nice people give one cake back to the girl at each bridge now the question is for the girl to be able to give grandma two cakes how many cakes will she have to leave home with