Amitriptyline is a tricyclic antidepressant that is metabolized to the pharmacologically active metabolite nortriptyline. Amitriptyline has half life of 21 hr, while nortriptyline half life observed after administration of the preformed metabolite is 31 hr. What will be the experimentally observed terminal half life of nortriptyline after administration of the parent drug amitriptyline ?