Suppose the estimated $20$ billion dollar cost to send a person to the planet Mars is shared equally by the $250$ million people in the U.S. Then each person's share is 
$\text{(A)}\ 40\text{ dollars} \qquad \text{(B)}\ 50\text{ dollars} \qquad \text{(C)}\ 80\text{ dollars} \qquad \text{(D)}\ 100\text{ dollars} \qquad \text{(E)}\ 125\text{ dollars}$
We want the cost per person, which is
\begin{align*} \frac{20\text{ billion}}{250\text{ million}} &= \frac{20000\text{ million}}{250\text{ million}} \\ &= 80 \rightarrow \boxed{\text{C}} \end{align*}