Final answer:
The model indicates a rate of change of $0.945 billion per year for call center revenue. Revenue in 2010 was $6.29 billion. The model isn't valid for estimating 2000 revenue as it would yield a negative value.
Step-by-step explanation:
The rate of change of revenue for call centers in the country, according to the model, is represented by the coefficient of x in the equation R(x) = 0.945x - 3.16. This means the rate of change is $0.945 billion per year.
To calculate the revenue for call centers in 2010, we substitute x with 10 (since 2010 is 10 years after 2000) into the equation, resulting in R(10) = 0.945(10) - 3.16, which calculates to $6.29 billion.
The model would not be valid to estimate the revenue in 2000 because when x is 0, the revenue model gives a negative value, which is not feasible for revenue amounts. Additionally, the model appears to only be calibrated for data from 2006 onwards and may not accurately reflect conditions prior to this period.
Summing up, the rate of change of revenue according to the model is $0.945 billion per year.