AHSME 1960 Problem 17

The formula $N=8 \times 10^{8} \times x^{-3/2}$ gives, for a certain group, the number of individuals whose income exceeds $x$ dollars. The lowest income, in dollars, of the wealthiest $800$ individuals is at least: $\textbf{(A)}\ 10^4 \textbf{(B)}\ 10^6 \textbf{(C)}\ 10^8 \textbf{(D)}\ 10^{12} \textbf{(E)}\ 10^{16}$