Use the models to find how long before the company's profit reaches $500 million. An investment services

Question:

Use the models to find how long before the company's profit reaches $500 million.
An investment services company experienced dramatic growth in the last two decades. The following models for the company's revenue R and expenses or costs C (both in millions of dollars) are functions of the years past 1990.
R(t) = 21.4e0.131t and C(t) 18.6e0.131t