Question: The US federal budget runs annual deficits of about $ 5× 1011. How high would a stack of $100 bills be if it contained this much money? Notice here, as is often the case in such questions, that you need to make some reasonable estimate of some physical quantity important to your answer-in this case, the thickness of a $100 bill. Most bills you see daily are not very flat, but you'll probably decide that a bill at the bottom of this stack would be quite flat!