David2403,
Please use an informative thread subject. This one could have been titled "Huge Prosperity drop from losing money".
The Prosperity calculation in Pharaoh is similar to that in C3, but there are significant differences. In Pharaoh, Prosperity can fall much more rapidly if you lose money in the previous year. On the other hand, Prosperity is calculated 4 times per year, so in 2 years you could raise Prosperity from 0 to 80 or more. Most players find Prosperity easier to handle in Pharaoh than in C3.