Question: Securities industry profits the securities industry experienced dramatic growth in the last two decades. The following models for the industry's revenue R and expenses or costs C (both in billions of dollars) were developed as functions of the years past 1985 with data from the U.S. Securities and Exchange Commission.

R(t) = 21.4e^0.131t and C(t) = 18.6e^0.131t

Use the models to find how long before the securities industry's profit reaches $500 billion.