Red Blood Cell project- exponential decay

My presentation is on the amount of red blood cells that die off in a 4 month period.  Every 4 months the body reproduces new cells to compensate for the ones that have died.  So I am finding the rate of exponential decay of the cells that dies over the four month period when the body has 30 trillion.  The rate of decay for the cells is 22.8%.  The equation is y=30 trillion(1-.228)t.  I have discovered that since we have so many blood cells, and they decay as such a large rate our body must produce 684,000,000,000 blood cells every 4 months.

exponential decay example

Luna has created a cupcake bakery.  Her sales have been decreasing by .66% each year over the last 5 years.  If she currently makes 50,000 dollars what will she be making in 15 years.

Phoebe's income- example of exponential growth

Phoebe has published a book and over the last 4 years the profit from the book has grown 2 percent per year.  If the current profit is 55 million dollars, what will it be in 10 years?