93. 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 of this area was 961,400 , and the population was increasing at roughly 9200 people per year. The average annual income was $\$ 30,593$ per capita, and this average was increasing at about $\$ 1400$ per year (a little above the national average of about $\$ 1225$ yearly). Use the Product Rule and these figures to estimate the rate at which total personal income was rising in the Richmond-Petersburg area in $1999 .$ Explain the meaning of each term in the Product Rule.