Answer:
If you invest $24 at a 5% rate during five years, you will earn:
$24 x (1 + 5%)⁵ = $24 x 1.2763 = $30.63
After 50 years, and at the same 5%, you will earn:
$24 x (1 + 5%)⁵⁰ = $24 x 11.4674 = $275.22
I guess that back then $24 was a lot of money, or at least a considerable amount since that was Manhattan's price (at least its equivalent price in trinkets). Or maybe he was a better negotiator than most modern politicians.