Costco€™s net sales are shown in Table 38 for various years.

Let n be Costco€™s annual net sales (in billions of dollars) at t years since 2005. A model of the situation is n = 8.7t + 34.4.
a. Use technology to construct a scatterplot, and graph the model on the same coordinate system. Does the line come close to the data points?
b. What is the slope? What does it mean in this situation?
c. Use the data in Table 38 to find the approximate rate of change of the net sales for each of the periods 2009€“2011, 2011€“2013, and 2009€“2013. Compare each rate of change with the result you found in part (b).
d. Use the model to predict Costco€™s net sales in 2020. Did you perform interpolation or extrapolation? Do you have much faith in your prediction? Explain.

Table 38 Costco's Net Sales Net Sales billions of dollars) Year 2010 2011 2012 2013 76 103