Using U.S. Energy Information Administration data for selected years
from 2012 and projected to 2040, total U.S. real consumption, C, can be expressed as a function of national disposable personal income, I, (both in billions of dollars) according to
C = 0.885I + 0.413

(a) Use a graphing calculator to graph this equation for the range I-min = 0, I-max = 25, C-min = 0, C-max = 25.

(b) The point (12.6, 11.6) lies on the graph of this function. Explain its meaning.

(c) What does the function predict the total U.S. real consumption will be when national disposable personal income is $18.5 billion?