Richmond-Petersburg, Calculus Question help

I have a word problem that I must be interpreting incorrectly -- I need to find the derivative using the Product rule. I know how to use the product rule, but I think my problem is with how I set up the functions based on the word problem.In this exercise, we estimate the rate at which the total personal income is rising in the Richmond-Petersburg, Virginia, metropolitan area. In 1999, the population in this area was 961400, and the population was increasing at roughly 9200 people per year. The average annual income was 30593 dollars per capita, and this average was increasing at about 1400 dollars per year.Use the Product Rule and these figures to estimate the rate at which the total personal income was rising in the Richmond-Petersburg area in 1999.What I have:f(x) = 9200x + 961400g(x) = 1400x + 30593My answer came to -$63.176 . I even checked using Wolfram Alpha and that answer is correct, which means I am most likely setting up the functions incorrectly.Thanks.