Question

advertising expenditures in the United States were $244 billion in 2000 and $245 billion in 2003. Let x be the number of years after 2000 and estimate advertisting expenditures in 2007.

Answer 1

I wonder just when the data were collected for the years; i.e., was it at the end of 2000 and at the end of 2003. If so, then 245 billion - 244 billion = 1 billion for 3 years or 1 x 10^9/3 yrs.
Advertising in 2007 = (1 x 10^9/3)*x years.
x = 2007-2000 = 7 years so
advertising = 244 billion + (1 billion/3)*7 = ??
Check my thinking.